clarity through all the confusion with my bf and ex's

[mas]

So i met this guy and started dating him.. We get along great and have a ton in common and always together. Only one problem. HIS EX! he dated this girl for like 4 years and apparently they always argued and she cheated on him in the beginnning and he never saw a future with her. They would break up and get back together on and off again toward the end. Finally he broke up with her. Next he dated this girl for a month whom he decided to only be friends with because he thought they were better friends and the ex and him would still hang out while they dated. Then a month or so later we met. The ex has stalked him throughout the relationship even after him telling her to leave him alone and that he is happy. He ignores her texts and phone calls, granted they have slowed down. He hasnt talked to her at all or texted the past 3 months or more. Here the kicker, she has become best friends with his older sister whom is 28 and going through a divorce, so they go out together and get drunk and she enables the sister from not being a good mother because shes at bars all the time and now living at home with her two little kids. So my question is, is that is this gonna ever stop, will he go back to her? He says that shes his e for a reason and i feel like if he wanted to be with her he would because she would be with him in a heartbeat. We have been dating about 5 months or 6 and i basically live with him. I have slept at his house every night for the last 3 months. We are constantly together and he talks about a future with me and living together. If she texts or calls he tells me and i get upset and frustrated. Its annoying. Does he really feel so strongly about me? I met his family many times and been to bars with his aunts and parents, or family dinners. I go out with all his guy friends and him. He started school since weve been dating and hes 27 and hasnt done that in the last couple of years. I have already graduated and am going back to school. Im just trying to figure it all out because w have a great time, we go to church together, we have the same values and views but this girl is really frustrating me and i odnt want to put all my heart into something and get hurt.