HELPPP

I need some advice. So my boyfriend and I are coming up on three years together and it's been the best three years ever...BUT THE SEX. We used to have sex all the time when we first started dating but I guess as the months went on we started to boot so it as much. We used to do quickies in his back room before I would go home and then do it again the next day now it's just once every week or every other week or even longer. I sometimes feel he's just not attracted to me anymore or he's just not in the mood. But I used to find his tissues under his bed or in the trash...like a lot of them. So I know he's masterbating. So now I feel even more insecure that he doesn't want to have sex with me but hell just do hi hand. WTF