When Ben cheated on Sera

The first few times I saw this film I assumed when he slept with that other hooker in Sera's house it was a moment of drunken weakness, fuelled by his resentment at her being with other men. It comes quite soon after the scene where he gives her the earring and she says "Ill wear it tonight", which doesnt go down well at all. Earlier on he had said he didnt have an issue with her being a prostitute but that scene seems to contradict that.

However I watched it again the other night and this time it seemed to me he actually did it because he realised drinking himself to death right under her nose was going to be too painful for her. When they are having dinner she asks him to see a dr. He says he isnt going to do that and perhaps he should move out, which causes her to get quite upset - it seemed to me this time that he realised he had to make her kick him out, that being cruel to her would be kinder in the long run.

Did anyone else have any thoughts about why he cheated on Sera? I guess his motivation is probably clearer in the book.