My boyfriend is into cuckholding

My (19f) boyfriend (25m) has a cuckholding kink. We are currently doing long distance until next year. He has been very open about this since we met (it's a fresh relationship) and I haven't done anything yet. I've been nervouse because I don't want to do it and he be upset after. He told me that he's experimented with it in past relationships and has reassured me many times that he is very much into it and wouldn't care at all. It's been a bit difficult remaining celibate as I have a very high intimacy drive, but I would go without. However, I'm planning on going out with an old fwb tonight, which he knows about . But I am very nervous. Any advice here?? Is anyone else in a situation? How did you ease into it? Thanks in advance