<human>: Can you summarize the given text in a few sentences?

My [23F] Fiance [24M] has been sexting other women through text and multiple websites and I just got wind of it. He claims he didn't physically cheat but in the messages I saw he was setting up plans to meet with these women. He works second shift and I am in bed when he gets home - he has been late some nights but claims it was overtime. We have 2 children together, as well. 
In some of the messages he was saying that I did not stay fit during my pregnancy (youngest is 6 months old) and am not fit now. I am by no means fat, but I do have to work on toning my tummy still. He was saying this to a single mom that he was flirting with online. All of his messages were very personal and against me. Some women wanted to add him on facebook but he said he couldn't because he's engaged and doesn't want me to find out. The women still kept chatting away! He also told many of them that he would much rather sleep with them than with me, and things along those lines.
I'm setting up an appointment to get an STD test done because I have no idea if he really did hook up with these women or not. I am scared, hurt, and feel like the most undesirable woman alive. 
I stopped wearing my engagement ring and he has gotten upset about that. He also believes I am more upset about this whole thing than I should be. 
Am I being unreasonable? I want to leave, but I am not bwck at work yet and have no family or friends. I am not sure where to go from here. I thought we had a great life and relationship.
<bot>: caught Fiance cheating, incredibly hurt, he says I'm overreacting, and I'm not sure where to go from here.