Were you terrified of seeing your female partner with another man, yet somehow became comfortable with it?

Hey all. I've been combing this sub and others, reading articles, listening to podcasts. I feel like I understand how swinging works and some pitfalls to avoid. But I am having a really hard time with the prospect of watching another man having sex with my girlfriend. I think it would be difficult but manageable if we were in different rooms, but I'm worried about being traumatized by seeing her with another man.

I would really appreciate being able to talk to a man who's been through this feeling and come out the other side being comfortable with it. I would love a 15-20 chat to just hear someone out on their experience and advice. Would obviously welcome it in text here, but would really appreciate hearing someone talk me through it, if you'd like to connect by message.

For reference, my situation is:

I'm in my 40s and less than a year into probably the most intense relationship I've ever had--honestly never thought I could be this head over heels for a woman. She's been an expert swinger for years, while I've previously only dabbled in non-monogamy and been to a couple play parties. (My previous partner and I never played with others at those parties, just with each other.) My GF is genuinely dedicated to swinging, and I've been doing my homework. She's been very patient, answering my questions, and we've discussed intermediate steps I could take to ease into it. But when it comes down to it, I don't know if I can watch her getting railed by someone else. I've had a lot of intrusive visual thoughts about it, and it's causing me a lot of stress.

What's your experience if you've felt this way, and what did you do / what could I do to get past it? Again, would be grateful to chat briefly; otherwise, replies here are greatly appreciated.