I have watched this movie probably 10 times (love Anna Kendrick), some things I noticed about Jamie. When he is singing the song about breaking his mother heart he names all the women he has dated or wanted to date. There are other times when he stops and takes a second look at other women. Cathy is aware of his sex problem just by the hints she gives.
So yea... I think Jamie can't keep his pants ziped
There is nothing that says he slept with all of those women. Could have just dated them, nothing more. The women he stops to give a second glance to could be women that he slept with, or thought about sleeping with. Could also just be eating up time before the next phrase and needed some "stage business".
What hints are you referring to? I never got those. Of course, I don't necessarily agree with you assessment that he is a sex addict. I think they are both people who are just never going to be happy with their life, and always need something more. The grass is always greener, as they say.