Advice please!🙏🏻

Al

OK, I will try and make this short... My and my fiance have been together 5 years. We have talked about trying new things in the bedroom for awhile now. When we first got together he brought up a 3some with another girl and I said that is a no from me , not something at all I feel comfortable with! This past month he has been saying he wants to try a 3some with another man, the thought of seeing me with another guy turns him on. I told him I have never been comfortable with a 3some but would be open to TALKING about it now. 2 days ago I was telling him I went to lunch with a male coworker, and he was like 'stop right there I got hard just thinking of you with another guy'... I'm trying to be ok with it, but here's my question, is it normal for a man to want to see his girl have sex with another guy?? Like to get turned on at the thought of me being with someone else?? I feel so conflicted! I want to try new things and am ik with talking about it and something we both feel comfortable with. but is this normal? Like a fetish or something?? Any thoughts would be appreciated