Is he (36M) just using me (39F) for a threesome with his girlfriend?

So I have this ex that I have always stayed close with. We haven’t seen each other for over 5 years but we never go more than a couple months without texting each other and checking in. He has a serious gf of 2 years. We have been talking a lot in the last year about meeting up. He knows I adore him dearly. He has drunk dialed me a couple times in the last year and told me he loved me, wants to have a baby with me etc…..
When we first starting really talking about wanting to meet up again he told me that he and his gf were looking for a 3rd and he wanted it to be me. I’m not into girls and I said no. He said she wasn’t into girls either but she wants do this for him. So fast forward to a couple weeks ago we were texting almost constantly over the weekend. That Monday rolls around and he tells me to skip work and come see him, just us. So I give in and do it. When I asked, before I came over btw, if his gf is ok with it he tells me he asked her if I could come over and she said as long as he wears a condom. And she doesn’t want it to happen more than a couple times before she meets me and we all have fun together.
I have never known this man to be a liar but I find this hard to believe a woman would be cool with this. Especially since she’s not into girls. Is he just telling me all of this to live out his fantasy? He’s never had a threesome before. I feel like he could be playing both of us.
Btw the sex was absolutely amazing. It was slow and hot and passionate.
He’s also been super quiet since tho. He’s only texted me twice in 3 weeks.
I’m really lost on how to read this situation.