Well if he always had girls over and was always texting other girls when spending time with you then yeah I wouldn't blame you. But If its just the fact that he has girls on his phone and that they come over some times then yeah its wrong.. you can just be friends with the opposite sex
The at his house part I kinda get. The in his phone part I don't really. Don't you have guys in your phone too?!
That depends on the type of and actual relationship he has with them. Personally I don't know why you'd want him back. He didn't put you first.
Do you have boys in your phone?
Only if you stop giving him grief for having friends, then he might do. But if he is anything like me, if you end a relationship, you don't go back. Especially if they are the jealous type. Sorry :(
Depends on the reason