that they can play with each other sometime
Does that mean casual sex? Could it be you just are not actually casual about sex and don't like this guy implying that your beloved is just for casual sex use?
On the one hand I am employing compersion, because my SO is enamored by the guy, and so I said "so go have fun."
It is not compersive to do things you are not actually happy with/willing to go along with. Are you actually good with your partner pursuing this Mr Crush guy for a casual sex relationship? Friends who share sex? Or just saying so because your partner wants to pursue Mr Crush guy? Is your partner pushing you toward things you do not want?
I had the scary thought today, that maybe a poly person who permits their partner to enjoy relations with other(s), is really just a tool, and vice-versa.
I don't think poly people are "a tool" just because they are open to loving more than one at a time and building their relationships in that manner. But that doesn't mean there aren't people out there in the world more than happy to take advantage of that. That also doesn't mean that there aren't people in the world who have less than respectful communication skills.
I asssume your partner arranged this communication opportunity so that you could let Mr Crush know your partner is not a cheater person. I assume you aren't just telling random people you are ok if they have casual sex with your partner without your partner knowing you are doing that!
Perhaps you would have preferred to hear something more along the lines of "Thank you for that generous willingness and letting me know up front how you feel about my developing a relationship with her" (implied: appreciating you and you partner) rather than ""yeah, I'll take advantage of that, sure." (implied: take advantage of your partner and take advantage of you too.)"
Is your partner a person or a thing? Is she a bike?
"Yeah, it's ok with me if you want to ride my bike."
"yeah, I'll take advantage of that, sure."
Is it Mr Crush treating your partner like a thing
, and that is the bottom line of what bugs you here? You could tell Mr Crush how you prefer to be communicated with. Could also take back the willingness before this develops further. Give you and her time to assess this potential Mr Crush person better. Could tell her
"Changed my mind! Hang on, horsie! He doesn't talk about you (my partner) with respect. I would not be ok with my beloved being with a disrespectful person! Need the clarify here!"