<human>: SO and I have been dating for about 3 months and it seems like things have been going pretty well. 

Last weekend we arranged to meet at a bar in a nearby city(where she lives) for some drinks and we would each bring some friends to make it a social thing. As the night goes on everyone is having a good time but one of her friends is kind of interrogating me, which is fine since she is just looking out for her friend. 

My group, myself and one other, took the bus there since we couldnt find a DD. Once it gets close to 2 my friend starts calling cab companies so we have a plan to get home. Usually I crash at my SOs place but one of her friends was staying over and I didnt want to impose and assume the same with my friend in tow. In retrospect I should have just asked.

I didn't want to be rude and ditch the only person that came with me so we managed to catch the last bus home. SO and I text where she mentions that the interrogating friend liked me until I left and is now super pissed. A few days later SO told me that on their way home interrogating friend, forgot to mention interrogating friend is a female, said "she deserves someone better" and kissed her/made out a bit. She said she felt weird and there was no emotion in it, it doesnt mean anything, sometimes that happens when girls get drunk etc....though she told me these things on the phone.

I am seeing her later today and I am still not sure how I feel about the situation. At first I didnt really think too much of it but its started to creep in my head a bit I suppose. My plan is to talk to her about it later in person.

Is this something I should be upset about or chastise myself for being a dumbass and leaving?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: SO's female friend drunkenly kissed SO after a night at the bar. I went home early so that my friend that joined us got home okay. Not sure how to feel? Could this be a warning sign for other stuff?