Advice?

Last night a girl I went to highschool with sent me screen shots of my fiancé asking her for nudes. I confronted him about it and he admitted to send that message to four people and one replied and they sexted over the phone. His phone was dead so as soon as it turned on I made him show me and all the messages were there. He was forthcoming once he was caught but I think he’s only sorry because he was caught. We have a daughter who is almost 2 and I don’t really want to leave him. I feel betrayed and hurt but I don’t want to break up our family. What would y’all do? We’ve been best friends since 6th grade and started dating our Senior year of highschool and have been together since. I never thought he would cheat on me. Is this even considered cheating? I feel like it is. I’m just so hurt and confused.