I think my fiance is becoming addicted to porn and masturbation. HELP?!?!?

My fiance and I have been together for 2 years. He has also been my best friens for 10 years. In high school he was very sexually active. Him and I never hooked up, we wanted to, but we cherished our friendship 2 much. After high school we went our seperate ways. After we turned 18 he wanted me to move in with him and he wanted to ask me to marry him but I had fallen in love with someone else. So he moved and a few nights later he got drunk and had meaningless sex with this girl and she got pregnant. His family wanted them to get married and try to make things work for the sake of his child. When I found out itkilled me bc I loved him and now he was gone. Well as e all know if u marry someone that u truly don't want to marry it usually falls apart. And it did. Shortly after the wedding his wife started cheating on him with several differnt men. And eventually she fell in love with one man. On my end I got pregnant and 2 yrs later the father became abusive and I left him. And when I found out that his wife was having an affair I was so angry bc I loved him n being hus best friend I couldn't tolerate it. So I Made him realize that he deserved btter and his response was that he wanted me th whole time and we've been together ever since. The 1st year wehad a decent sex life. But soon came the excuses as to y he couldn't have sec with me. I started to feel that he was cheating but I was proven wrong and then and I still feel that he isn't attracted to me anymore bc I gained a lot of weight durin a twin pregnacy and I feel like I'm not good enogh for him. So eventually I just decided to respect the fact that he just doesn't have the same sex drive as I do. Well about 6 months ago I started catching him masterbating. At first it upset me because I didn't understand y he would do that when we have great sex. But after getting another males opinion I understood that sometimesmen just like to do it. So I let it go. Well our love making started to get far n few between.