I walked in on my husband with another man.

I am 8 months pregnant and we have been together since I was 14. We've never had any serious real issues and never any cheating. So today I came home and found him in the bed with another man (his barber) having sex. At first I thought maybe my eyes were deceiving me when I walked in. They didn't see me so I tipped toed out the room and headed to the kitchen to grab something to throw at them. I proceeded to boil some water. I walked up the stairs and made my presence known and the only thing that kept me from throwing the water was the fact that my son came in the room. I am furious and it took everything in me not to murder them both. He's been telling me it was an experiment and his barber told him that it would calm down his nerves and he didn't think I would mind. Sure! That explains why he lied and told me he would be working over time today. He didn't expect me to come home early. And it pisses me off that my son was in the other room while this was going on. He could have walked in on them before me and would have been so confused. My husband is begging me not to leave and is begging me for counseling. I packed up my son and I'm staying at my mothers until further notice. Should I give him another chance? 
UPDATES:
My son is 13 and is old enough to stay home alone. He is not speaking to his dad and is very angry. I keep trying to give him as much fun time as possible since this entire situation is traumatic. He's told me that he didn't even know that my dad had the barber over because he was in his bedroom sleeping with his headphones in his ear. The only reason he even came into the room was because he heard my screams. 
I know that pouring boiled hot water on someone is wrong but in the heat of the moment I wanted him to hurt as bad as I was hurting.
My husband keeps claiming this was a one time thing and his barber also promised to give his whole entire family free haircuts for life if he tried it. I feel like he's full of shit and he's been sleeping with this guy a long time. They always hang out and go on trips together. 
I've decided to file for divorce. I don't even want to give him another chance. At first I was considering it but he just keeps lying to me. I do not trust him.
My mother never liked him and is overjoyed we aren't staying together.
My husband left our home and wants me to come back to live there.  He's living with the barber for now apparently.