I think a lot of people dislike Preston as he is the only good looking bloke in there (or the least ugly, depending on how you look at it). So, he has a lot of people supporting him because of his looks (like Shayne in X-Factor, Anthony in BB6 etc.).
I don't see his behaviour as being any worse than any of the other housemates.
As for his girlfriend, has he actually done anything wrong? It's a pressurised environment to be in and he is drawn to Chantelle - same age group and she's a nice girl to be around. His girlfriend must be hating every minute of it (and according to things I have read they have been together a year after he split from his fiancee of six years so he hardly seems like the playing the field type) but I do think Chantelle has behaved very well - not remotely stereotype chav-like. Unlike the oh so well spoken Faria of course, who still does not see anything wrong with shagging Sven when she knew all about Nancy his partner of many many years and then selling her story.