Just found out i got cheated on💔

Just found out that my boyfriend that I’ve been with for 5 years cheated, but this time for real. Why for real?Because the other times he would just add girls or download those apps where u can talk to girls and he knew it would get me mad bcs im insecure and he knew i didn’t like it he would still do it even after he promised he wouldn’t... but this time he cheated fr and with his sister in law sister. He would met up with her and do the what cheaters do. The thing that hurts is that we have a5 month old baby. Idk what to do or how to feel rn.. I am still in shock. I told him and he cried and beg to not leave him. Idk what to do one part of me is telling me to not be stupid asf and leave and the other part of me is telling me to stay bcs it would hurt seeing him with someone else.. i am so confused but ik leaving is the best for my soul