WWYD if your boyfriend is cheating on you?

Hi! Ive been in a relationship w/someone i shouldnt have even gave a chance.. i found out my boyfriend is back dealing with his ex girlfriend.. he was supposed to come to my house 3 times in a row but instead he just disappeared. I drove around looking for him the whole morning & couldnt find his car.. he came over to drop his laundry off to me so i could wash it & his ex girlfriendcalled his phone & i seen it. Later that night he came over & left his phone unattended & i was able to find out on those two out of three days he was having some type of encounter with her.. i want to approach him & talk to him about it but im not sure how to bring it up without cursing or adding fuel to the fire... he'san aggressive/physical person when SUPER upset & i dont know what to do .. my heart hurts soooo bad. Ive been nothing but faithful to him & theres a possibility i could be carrying his child since my period hasnt came & we got a positive pregnancy test.. any advice on what to do ?