Ex girlfriend behaviours

Was with this girl for about 6 months, ended things and was on good terms with her because we are in the same friend group (people that I go to bars/clubs with, not hanging out that frequently).

After we broke up we would go out together with our friend group to clubs and would both hook up with other people but on a few occasions danced and kissed each other in a spur of the moment thing but nothing else developed, this was all while we were both single.

I started dating someone else who is now a LTR and the first time I introduce her to my friend group my ex was the first to talk to her, I asked what it was about but nothing serious, just a bit odd. That night my ex was also lingering around me wanting to dance and being more affectionate than normal when we were both single; this happened a few times when I was with my LTR early on.

A few weeks after I was with my new gf, my ex started to date a guy that is friends with my gf (met in the club when both groups were out, coincidence or not idk). So we are now both in relationships but still see each other in social events and pretty much never talk or go near each other respecting both of our boundaries.

Last week however we were both at a bar with our friends with both our LTRs being out of town, we are both friendly with each other but later on in the night she started to become more affectionate, sat beside me, was laughing at everything I said, making extended physical contact on my arms and thighs which I found inappropriate but didn’t say anything. Then later on in the night everyone was going to a club but I had an early start the next morning so I refused. My ex was very persistent on me coming though and asked several times to come trying to make solutions but I still refused.

I would be lying if I said I don’t have any feelings for her still as she was one of my earliest relationships and I see her quite often. However she cheated on her bf before me which I didn’t know before I dated her. I’m happy in my relationship but just wanted to understand the psyche of why she acts this way and it has been playing on my mind recently. Anyone had any experiences like this before?