Husband cheating

Literally just found out my husband is cheating on me. My son was playing in his work bag and pulled out a letter that she wrote him. We’ve been together for 11 years. How could I be so stupid. We have an 18 month old son, and we’re trying to have another baby. I don’t even know what to do right now.

I just texted him and told him not to come home. I don’t even want to talk to him. He’s probably with her right now.