Best friend turned secret lover

[Little Kitten]

Okay so I've been friends with this guy for a few years. We dated last year and have gotten rather close. Even after breaking up we were still rather close and he told me he didn't see me as an ex. We even saved each others lives before and doing so we confessed how much we loved each other. We fell out for about 3 months over something stupid and didn't even see each other...but the one day I decide to go to his house and take care of his mom...he's in my face wanting to know how we were gonna fix our situation and how things would be different. His mom told me that he was still in love with me but I didn't believe it. He and I stayed up until 4:00 in the morning having a serious talk and one thing led to another and we ended up sleeping together the very next day for 3 days in a row. Now the bad thing is he has a girlfriend which he tells me isn't a serious relationship with him. He's been wanting me to stay the night at his house which and takes me to the hospital to visit his sick mother and help take care of her....he won't even let his girlfriend do it. My mom and his mom says he's gonna break up with her soon because he has feelings for me...but his situation is all too confusing for me. He doesn't even stay on the phone with his girlfriend when I'm around which I told would be completely fine with me...now he's been checking my phone seeing who calls me and if I answer my phone he instantly says, "Who is that?" I'm not technically with him but he goes though my things as if he was my boyfriend...he goes through my phone...through my purse and bags...not that I mind...I just find it unusual for a person whos just supposed to be my "friend" Why is he doing this?