A little back story

My girlfriend Jennifer (22) and i (23) have been together about 4 years. My friend jason and Jennifer didn’t get along when we first got together but they have since became goods friends and she jokingly refers to him as her “other boyfriend” from time to time. He will also do stuff like walking by he might slap her ass and she doesn’t mind, or for instance she got mad and said “fuck me” when she got our sonic order wrong and he said ok bend over and she bent over jokingly, but that’s as far as it’s ever went. Until last weekend We were at a party at my house and it’s a pretty normal night drinking listening to music and what not. Jason and Jennifer are their usual self he asked her to get him a beer and when she bent over he started dry humping her and she let him. (I found this out after the fact but it is a pre cursor to the next paragraph) At some point Jason walked to the side of the house to piss and i was inside and i have since found out that Jennifer walked around the house with a friend of hers and acted surprised to see him there and then (according to her friend) said “put your dick up we are trying to get the water hose” and he told her “the water hose is right here” referring to his dick and then told her to suck it and the friend to be the lookout. Shortly after she gets done sucking his dick, he comes up to me and says “hey bro let me fuck Jennifer” i didn’t know what had just happened and we were drunk so i told him to try it and if she wanted to go ahead (not thinking she would actually let him). About 30 minutes later i didn’t know where either of them were so i went back inside and figured she must be in the master bathroom, and she was and so was Jason. I walked in and he had her bent over the counter and i said “Jennifer what the fuck” and she looks dead at me and said “don’t stop fuck I’ll be out in a minute”. We have not spoke about it yet and i don’t know what to make of it