[MFF] this is my first time posting about this but my gf hit up my ex for a threesome for a birthday present for me!

I’m nervous af! It’s my first threesome and my new gf finally gave in and I’m not sure if my ex is fucking with me or not because my new gf started texting her to seduce her and she was way to receptive of it??? Is my ex fucking with us or does she miss my dick that bad? We were on and off for months so I wouldn’t be surprised if she missed my dick because when I first started dating my new gf she wanted to hook up even tho we broke up but I told her no because it wouldn’t be fair to new gf without her permission and at the time new gf was insecure since my and ex and I had a lot of history that I wasn’t over at the time and we had only talked for about two weeks. Give me advice!!!