Threesome with a bi guy and his GF?

I went to school with a kid and then went to college. I'm a college freshman and he's a high school senior. He's bisexual and him in his gf are into threesomes. He doesn't like having sex with guys in them though because he fears them touching his girl so its normally 2 girls, the 2nd girl having a strap on. I kinda pointed out to him if he got a gay guy... he wouldn't want to touch his gf. He said he'd think about it (NEVER thinking of myself as the "gay guy" in the situation) well a month later I get a random text from him asking if I wanted to do a threesome with him and his gf and I was kinda in shock. We are all in agreement that me and his gf would have no interaction at all during it

Still not sure how I feel about this whole situation... but I haven't gotten any in a LONG *** time so I'm sorta open to it.