What do i do?

A little back story first I have been with my so for almost 13 years we have 2 children and until recently had been TTC but I just got a new job and on my 4th day of work I found out he was texting a girl from his job he gave her his number after she asked him if he ever cheated on me or talked to other girls mind you she has seen me and my children everyday when we pick him up from work. I seen the text messages and it was little things like what's your favorite show and her saying that she feels special because he told her he hadn't talked to another girl in a long time. As far as I know they only texted 2 nights while I was as work. One of her messages asked what he wanted to come of them and he said no fling but no matter what were friends till the end. When I confronted him he said he didn't know what he was thinking and made a big mistake. I'm so devastated and confused as to why he would do this to me! I do everything from cooking to cleaning and like I said I just got a job to help financially. I don't know what to do?! I have to take him to work every day knowing she's there and I just don't know if I can handle it but he needs his job to support his children at the least. What do I do?