I've caught feelings for a FWB

We met last year. He's 20 years younger and has a thing for older guys. I'm in my 50s. But he gets around. Turns out he's slept with many guys I know, including my cousin, who's around my age. And they warned me: Have fun with him, but don't get attached. He's introduced me to his social circle. We have lunch occasionally. But I know he's seeing other guys. He's very open about it.

I've kept telling myself that I don't have genuine feelings for him, that it's just the excitement, that he's just my type (otter), that I don't know him well enough . . .

But I'm lying. He's increasingly on my mind a lot. I feel very affectionate towards him. But I know he's not equally interested in me. And it hurts.

I feel like an idiot, and I wish there was an Off switch for this.