I cant believe my husband done this

Ok so things have been really good with my marriage recently I've been married for 3years together for 8 have a 6 year old and a 9month old. So last night we went to the bar for a few drinks with friends and they came back to our house. 2 of 4 friends left and I was going to bed I had work dismorning and night feeds with the baby. I got ready for bed and decided to go for a cigarette before hand I went to walk into my sitting room and notice my husband and basically best friend having sex. A good guy friend of mine was in the same room who had also just had sex with the same girl.

I really dont know what to do he swears he doesnt remember but they have history.

I'm not originally from America I'm Irish so I have no family here and very little support friend wise.

It hurts so bad as I just gave birth 9months ago and also just had a misscarriage and surgery to remove my babys remains (3months pregnant baby boy also). I dont know what to say hes acting as if nothing happened.