I think im going to end up cuckolded? [Threesome]

This happened a couple of weekends ago but me (24) and my GF (22) had a threesome with a Black guy she works with (he's 38).

Everything started normally, we both made out with her while we undressed. The issue is once I saw how big he was vs me I literally couldn't get hard no matter how hard she tried. He had to have been atleast 8 inches and I'm under 4 inches a bit.

He started fucking her and I ended up making out with her while she came on his cock 3 or 4 times, it was super hot but I still couldn't get hard. Eventually I left the room and jerked off down the hallway trying to get hard but accidentally came hearing her cum again. I didn't know what to do so I just sat there until they finished.

Eventually once they finished I checked on them and saw them cuddling in the bed, sleeping. I just left them alone and slept on the couch. What shocked me is that I woke up in the morning to the sounds of her getting fucked by him again, without me there at all. I ended up getting hard seeing this and jerked off, they didn't see me. He finished and I heard them making plans for him to come over this weekend!

I haven't spoke to her about it, she's been super loving since then but we've also had 0 sexual contact since then. I think I'm about to get cuckolded whether I want it or not