The surgery is completely life changing for both of them, I don't think that's really comparable with saying he stays despite her personality. He always has the option of calling things quits and it being a relatively minor thing as is, but leaving someone with cancer? That takes a lot of balls, then you add them having gone through surgery like that? Most people would feel bloody awful doing that, but equally, many people couldn't handle it and that isn't a 'kind'. He shouldn't be judged for that, whatever else you think of him. At the moment this may just be a current casual relationship for him, but this is likely to bring home a huge reality for him as to whether he really is in this for the long haul and what that means for them both.
Plus you don't like Tiffany's personality, he obviously does, so that's irrelevant really, you can't base anything off that.