Oh I hear ya and fully understand that.
For me however, it is the intimacy that is the turn on. I want to see them embrace and kiss deeply when they meet. I want to see her glow when he texts her and tells her he can't wait to see her again. I want her to tell me that "he" wants me to buy her some new lingerie for their next encounter.
And after their encounter, I want her back in my arms telling me she loves me.
That's the "turn on" for me.
Realistic.....probably not, but those are the thoughts that make me stroke just a little bit harder!!!!!