He may be doing this to get back at you for breaking up with him in 2007, he may want you to feel the same pain he felt when you broke up with him. What you need to do is be honest with him about the way that you feel and apologize for breaking up with him in 2007 and tell him it was the worse mistake of your life and then tell him you want the two of you to be together and if he doesn't want to get back together there is nothing else you can do if he isn't willing to give the two of you a chance and stays with his current girlfriend. What you are going to have to do is make up your mind how much you are willing to take from him and if you are willing to come second or even be his mistress if you are not willing to be any of those and you have told his girlfriend that he is still seeing you along with her then it's time to break away as painful as that may sound it is something you are going to have to do or else he will continue to have you on the side and not make a commitment to you. You need to cease contact with him if you tell him how you feel and he does nothing about it. He may be marrying her because of the way you have stopped communicating with him so contact him and tell him how you feel about him make this your last ditch effort to win him back.
It's because he wants what he knows he cannot have which is "you" he knows your families do not want you with each other and will make it hard for you. The current girlfriend is his best bet for him in his eyes and this may be why he might ask her to marry him, his family could possibly be pressuring him into doing so that is why is it crucial for you to talk to him and see where things stand and ask him to please finally be honest with you. You broke up with him in 2007 which made him want to pursue you and once he got you he was with someone else and he didn't want to stop seeing you so now he wants his cake and eat it too. It's up to you to decide if you are going to allow it to be this way for the rest of your life or when it's time to cut your loss' and move on but I would talk to him and see what he says about everything.