Did Lan Yu date anyone else during Handong's marriage?

Thanks. Between the time of my question and your answer, I've manage to get hold of the english translation of the novel (thanks to mrbgomen). So, I've already gotten my answer and know the original story. But I still welcome your reply (because it gives me a chance to tell someone what I felt about the novel and movie, haha.) and appreciate your effort (at least u care enough to help a fellow viewer understand the movie better )

I think differently regarding the novel. I think it's better than the movie. Yes, the novel can do with less sex scenes or less graphic one, but the novel is also more detail and in-depth and at some parts more logical than the movie.Even the sex scenes reveal something about the characters' personality, relationships and feelings.

More logical:

Lan Yu's relationship with Liu Zheng and Liu Zheng's personality. In the movie, Liu Zheng seems to be a really nice guy and Lan Yu seems to trust him a lot. At the 4 months later scene, Lan Yu told Handong that Liu Zheng is a nice person. During their fight at the elevator, Lan Yu shouted at Handong that he will ask Liu Zheng to withdraw his (Lan Yu's) money from the bank to give back to Handong. Lan Yu even trusts Liu Zheng with his money. Lan Yu is also Liu Zheng's friend's brother in the movie. Why would such a good man as Liu Zheng and with his relationship with Lan Yu pimp Lan Yu to other guy for money? Isn't it more logical for Liu Zheng to lend his own money to Lan Yu until Lan Yu gets a part-time job? In the novel, Liu Zheng is not as nice. He often helped Handong look for 'fun'. Lan Yu is only a destitute young man he just met in front of a Business Centre. So, it is more logical that he would pimp Lan Yu to Handong, because Liu Zheng has often look for one-night-standers for Handong and he has no relation with Lan Yu, so, has no obligation to look after him like in the movie.

Lan Yu told Handong he didn't contact Handong because he has lost his number. When I was watching this scene I wonder 'why didn't he just call Liu Zheng to ask for Handong's number?'. Maybe the movie Lan Yu is too shy or don't know how to approach Handong. So, he just left it be when he lost the number.

But in the novel, it is very clear why Lan Yu didn't call Handong. He was busy at school and his part-time job and I think he also want to be able to earn his own money first before approaching Handong again so that he can develop a non-monetary relationship with Handong. He didn't want Handong to think he only wants Handong's money.

More indept and detailed plots and characterisations:

Lan Yu
Yes, Lan Yu in the movie is basically the Lan Yu in the novel. We see Lan Yu's pride in the movie and his refusal to use Handong's money. We also see Lan Yu's sincerity in the movie and his true love for Handong. But in the novel, this is even more apparent plus we see Lan Yu's stubbornness and bravery but also recklessness (during the Tiananmen incident). Lan Yu in the novel was also willing to endure more than Lan Yu in the movie. The movie Lan Yu left Handong twice. Once when Handong cheated on him with that muscle guy and another when Handong want to get married but still want to remain with Lan Yu.In the novel, Lan Yu loves Handong so much that he still remained with Handong when Handong want to marry and I remember he still stick with Handong when Handong cheated on him with the drummer.But he stood his ground when Handong wanted him to quit his part-time job because a non-monetary relationship with Handong is important to him (Lan Yu in the movie was more willing to accept Handong's gift than novel Lan Yu, who finally relent just to keep Handong happy). He also didn't beg Handong when Handong said dumped him. I do not know which Lan Yu I like more. I like that the movie Lan Yu keep his dignity and was able to leave Handong and Handong wronged him. But I also like the novel Lan Yu who was willing to endure more to be with Handong. Another thing I like about novel Lan Yu that is not apparent in the movie though is Lan Yu's honestly. The novel makes a point to emphasize this many times. Lan Yu never tell lies. When Lan Yu didn't want to tell a person something,he just keep quiet. This is one of the personality of Lan Yu that attracts Handong.
I like the part in the book where Lan Yu only took the amount he asked for after the first night eventhough pay him more and I like that he leave a note telling Handong that he will even pay back the 1000 yuan service payment. I also like the fact that Lan Yu searched out Handong himself after he was financially independant instead of leaving their meeting to chance like in the movie. The novel also give some possible reason why Lan Yu loves Handong so much. 1) Their 1st gentle love-making (Handong made sure that it's gentle so that he can manipulate Lan Yu easier next time). 2) No one has threated him as nice as Handong after his mother's death. Lan Yu's background story also tells a lot about why he has to prostitute himself in the first place.

Handong
Like Lan Yu, Handong in the movie is basically Handong in the novel. But Handong's background story (his sexual experience during his youth) add more to the personality of Handong. Handong psychological struggle with his sexuality was also dealt with more,like him seeing the therapist and trying to convince Lan Yu that homosexuality is a mental illness. In the movie, it seems like the only problem in the relationship was Handong's inability to fully come to terms with his sexuality, that Handong was the only problem and the surrounding people have no problem with his homosexual tendencies. But this was not the case in the novel. External pressure was also great, especially from Handong's own family. His mother practically went hysterical and called her son shameless and non-human when she get to know of Handong's relationship with Lan Yu and his own sister look at him with disgust. I hope the movie has included this aspect in the movie. This is the intention of the author. To tell how society's prejudice bring pain to these minority group. This external pressure plot also made Handong's choice (of marriage) look more sympathetic. The only people that accepted his homosexuality was good friend Liu Zheng and his 'decadent' friends who also don't mind him playing with young girls and having 1 night stands.The novel also shows how ruthless a businessman Handong is and how being with Lan Yu soften him a bit.

Overall Plot:
Like I said above, the story emphisize a lot more on the pain society's ignorant (like all gays have aids) and prejudice bring to the minority group.
I also wish the scriptwriter has added the part about the therepist in the movie. It again shows the ignorant society has towards homosexuality back at the 80's. But this is not the main reason. The main reason is I like the dialogue when Handong want to persuade Lan Yu to go see the therepist ("U actually think yourself is a girl" "I don't" "Then why do u only like men" "I only like u"). I also like the all the steadfast "I don't want.."s Lan Yu said to Handong. I don't know why, but reading himself saying this endears him to me very much.
The plot in the story also show the changes of ther perception of the public on homosexuality. In the beginning, Handong an Lan Yu can only show effection behind close doors. The Tiananmen incident is a big leap in their relationship because that is the first time they hug in the open (but still under the shadow of the night) and near the end, they are finally brave enough to hug in bright day light. This might show society has become more tolerant or Handong and Lan Yu has become braver.
The Jing Ping subplot in the novel allows us to know more about this woman and why her marriage with Handong failed (I actually felt sorry for her although I don't like what she did to Lan Yu).

You must see past the 'porn' to see the touching story in the novel. Like I said in the beginning, the sex could have been less graphic and the number reduced (so that it won't turn some readers away from the story the author mean to tell. Not everyone is comfortable with so graphic depiction of sex), But sex scenes are not mindless porn put in just for porn's sake. Honestly, I can get more from the sex scenes in this story (the state of mind of the characters and the condition their relationship in at that time and the personality of the characters and the dept of feelings the characters has for their bed partner) than from the sex scenes in the English romance novels I've read (Judith McNaught, Jo Beverley, Johanna Lindsey etc).

P.S. I may like the novel more, but Lan Yu is still one of my all time favourite movies, right up there with 'Grave of The Fireflies'.