I turned down sex, did I make the right choice?

I'm pretty sure this would either go here or real life stories but I'll post it here to be safe. 
 
Went to a club in town with a few friends last night. We're drinking, having a good time, I wonder off for an hour or so and next thing I know one of my buddies has two girls just on top of him and I come over and the more attractive one of the two practically jumps on top of me (or so I think she was the better of the two, the alcohol might of gotten to me) either way we just start making out and on the dance floor hitting it off grinding on one another before we all just kind of stopped and I see my girl give somewhat of a weird look to her friend. So we all get our coats and head outside to get a cab and what not, found out that the girl I was dancing with has a boyfriend, which was really bothering me... my friend and the girl he was dancing with get in a separate cab so it's just me and the girl. We got a cab a few minutes afterwards and she was trying to make out with me for the entire duration of said cab trip, but my level of drunkenness just plummeted and I wasn't feeling it, she was trying to get me into her place but I just didn't feel right about it.
 
So we said our goodbyes what not and the taxi driver just starts digging into me about how I didn't go for it and said he wouldn't of charged me if I had went with her (broke enough as it fucking is I would of ran with her if I had known) but still I just had the stance that it wasn't right due to the fact she's in a relationship. Either way didn't really think about it that much and eventually got home and just rested up, but it's just been bothering me so much today to the point that I'm typing about it at this very moment lol. My friends actually gave me the hardest time in the world today about how I just didn't go for it, and despite my reasoning that it didn't feel right they still dug into me and eventually I thought... "she gave my friend a handjob in the club" which then led me to believe this "relationship" the girl was in wasn't very solid and I assume she has done things with several other guys other than her boyfriend. 
 
So I've just been bothered by it so much today, in one sense I dodged a bullet in the case that by the looks of it she's been around... A LOT, but the other side of me is saying that I should of just gone for it in the sole fact that my reasoning for not having sex with this girl was that she had a boyfriend but yet again she's probably done this with so many other guys. Now I'm just gonna go hit the vape and try to sleep this off