I am not sure how best to answer you or what kind of answer you really want to hear.
Different people certainly have different fetishes- It sounds like the man you are talking about has a fetish for group sex and voyeurism watching...
As a general rule about sex I usually tell people that if they feel comfortable about something, and it is SAFE, and they are consenting adults , then do whatever you are comfortable with. But in this situation 1) you don't sound to be comfortable with this and 2) it is NOT safe to be having sex with strangers- In fact that is just plain stupid and unsafe.
You obviously have a choice to make, but I would not place yourself at risk , or do something you don't want to do. Either the guy gets counseling form a specialist , or you may need to make a difficult decision.
Be safe yourself!
Always ask if you need clarification/more information.
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