I agree with most of this except the part about someone fantasising about someone else while having sex with you. I’m sorry but no. I’d not be OK with this. When someone has sex with me I want it to be because they want sex with specifically ME and not with some fantasy woman in their heads. If they want the latter that’s what masturbation is for. If you have sex with me, be present. And I’ll be present with you.

That’s my personal sexual boundary and it doesn’t make me a restrictive lover to say it.

Maybe having your partner have sex with you while imagining (wishing) he was having sex with someone else works for you. It doesn’t for me. In my opinion that’s nothing more than masturbation with another person’s body. If a partner of mine wants to fantasise about someone other than me, that’s fine. We’re polyamorous. But NOT while we’re having sex TOGETHER.