My boyfriend masterbates everyday in the bathroom, iin?

My boyfriend and i have been together for 4 years, i was married before and have 2 kids with my ex. My boyfriend and i have 2 kids together, so i have 4 kids, lately we havent been intimate, i have confronted him so many times about jerking off to porn, most times he lies about it but then eventually admits it and apologizes for it and says he jerks off mostly without porn, yeah right. now every morning when he gets up for work he spends about 40 minutes in the bathroom, i can hear him jerking off and lately hes been using lotion or something cause the sounds sound wet. i hate to spy on him like this but it makes me feel that maybe he isnt into me anymore, i feel like he might have met someone, he is constantly on his phone, hes says he is just reading forums, he deletes his history all the time so i cant prove that he is doing anything wrong, but he has crossed so many lines in the past that i feel i can not trust him anymore. maybe he isnt doing it as much as i think, but my gut feeling says otherwise, he has said this jealousy thing is going to ruin us. We have a family together an plan to marry in the spring. should i cut him some slack??? or should i trust my gut that something just isnt right??? please help me!!!