Last scene confused me

No she didn't. She lied. Trisha said as such to see if Sid would give her a second chance, just as he was asking her for.

Probably not, she just did what he did and was in a hotel room by herself and made an excuse to stay there
what was awful is she lied to him about having an affair, which is completely different from what he did, that ruined the movie
i liked the movie up until this lie that ruined it for me

It is never about what happened, it is only how you look at it!