Can't get over his affair

When I was pregnant with my son, I discovered my husband was having an affair with a coworker. He ended it, we went to counseling, things have been great. Now, I am pregnant again, and I keep having nightmares about his affair. It is giving me horrible anxiety and making me so depressed. I don't know how to get over this. I keep thinking it's going to happen again. Has anyone had experience with this before? How did you cope?