Is this a big deal idk

So my bf got a new job and made new friends there was this one girl in particular that he got along with. One night not long after he started he went out with her and two other guys after work like 12am. He didn’t tell me he was going out with anyone and told me couple days later. But so he says they all got dinner he paid for her and then they went out drank at a park apparently, smoked and shit and I was like uh okay fine it felt really sketch cause since getting the job he had been acting different but I assumed it was cause he was stressed or what ever. He acted so casual about it but something felt wrong. But so like two months later he confessed that she had been flirting with him and they had made out that night. He says it was nothing and it was awkward after and they laughed about it but omg I feel so disgusted. Like I don’t wanna even think about her flirting with him and then him buying her meal and then them kissing idk. Oh and apparently she drove him home drunk and dropped him off. Which scares me even more cause I don’t know if they went inside and did more shit!! He says he swears they didn’t and it was just a dumb drunk kiss. His literal exude was that he always just naturally kissed me all the time without thought he did that to her from reflex but idk what to think cause I’m not sure I entirely believe him since he was able to hide that part of the story so easily.