What Should I do About My Ex?

Im 18 and I have been dating a 25 year old guy for the past 6 months. I have known him for the past 4 years and we finally decided to get together. It became a shock to me but I actually feel in love with the kid. We broke up like almost 3 weeks ago. I was actually living with him and installed cable into the house...which is actually his moms house who i love. When I moved out I decided to keep paying for the cable for his mother who is refined to the house due to illness. I really like spending time with him but he started seeing his ex girlfriend again and whenever she is around he pretends I dont excist ( she doesnt like me, and didnt want me to be with him cause she has always loved him and he loves her too....yet he talked bad about her the whole time we were together listing all her flaws) ...though he says Im over exagerating things. When we broke up we decided to be friends though it seems like its only friends when she isnt around. I dont know what to do. I miss him...as a friend and i feel like im losing that to. This whole situation is insane. I need advice. Thanks