How do I react to him admitting to almost cheating on me?

Confusedgirl
My boyfriend who I have a baby with, I recently found out he was going to cheat. I saw a picture of a girl in his his cell phone ( 3 pictures ). An he admitted to me that he thought about cheating on me with her. He works with this girl. An he said that we have been arguing a lot lately and he wanted to escape. But he never would tell me that something was wrong I figured something was wrong, I kept asking are you happy, are you ok, he would reply with I am fine of course I am happy. He told me that they only talked at work but I found her number in his recent calls when I found the picture, and he said no that it was work related. I don't know what to do I have a baby with him and he is begging me to stay (crying). The thing that sucks I work at the same place I am about to go back to work ( maternity leave) and everyone has been seeing them spending together, and I look stupid. I go up there with the baby smiling and proud of being with him, and they are thinking you are so stupid he doesn't love you. I just can't believe he wants to be with someone else, I know we have problems but not that bad , I have never thought about cheating on him just because things get a little hard. I am just so STEAMED. I don't believe him I think he did something with her nothing making sense. HELP I don't know what to do?
How do I react to him admitting to almost cheating on me?
14 Opinion