Cuckholding Kink

My boyfriend, who’s also my “daddy”/ dom, has this kink. I’m not into it at all, and the idea of having a guy in me who isn’t him gives me extreme anxiety. He wants me to record it and send it to him, saying “if I have just 2 or 3 videos I’ll never talk about it again. He just doesn’t care anymore that I don’t like it, but then he will say “sorry” and “I love you” because he KNOWS I absolutely hate it and get 0 pleasure from it. I’m getting anxiety just typing rn. Idk what to do, should I just suck it up and do it one time with a stranger? He literally can not understand why I wouldn’t want to do it because “it’s just sex”.