Husband Cheating

So my husband worked at Wal-Mart for 2 years. He had made friends with one of,his coworkers there which is another girl. They first started being friends on facebook, and then gave there numbers to each other. At first all they talked about was work relates things. After he quit Wal-Mart they stayed friends. They ended up getting close. They both started having feelings for each other. Barely hung out, but they would text each other a lot about stupid things. Then after they both realizing it that they had feelings for each other. There was one night when they were leaving and saying goodbye they hugged each other like you do in a relationship. She kissed him on the cheek and then they ended up giving each other a peck kiss on the lips. He says that's all that happened. I really don't know know what do to about it all? Im 24 weeks pregnant with his chold. Any advise would be appreciated.