Threesome issues

So my boyfriend has always fantasized about threesomes, with a guy or girl. I finally caved in and found a girl, as guys make me uncomfortable, but... I’m still not comfy. We tried this before with another couple online who was incredibly into BDSM, and outside the chat he was really mean, telling me to be more active, send more nudes, even comparing me to her and trying to make me sneak out. I have NEVER seen him like that. It never went anywhere. I know he’s wanted this for years, and that might be it.

He complimented the girl a lot and it made me feel super depressed Because he kept comparing me to her and I’m scared he will do it again. How can I get over this?