My best friend of two years (20f) and my close friend/flatmate (20m) want to bump fronts and the idea of it makes me feel weird. 
They're both newly single after long term relationships and aren't after anything serious, just a one time hookup.
They met each other through me.
She asked me what I thought about it and for my blessing so to speak, but I said that it makes me feel weird and that I'm neither for it nor against it but she keeps pressing me about it. 
I've asked them both why they can't just pursue other people but they said its because they know each other and the attraction.
I'm not into either of them.
They said it wouldn't damage our friendships with either of them and it wouldn't ruin our friend dynamic but i'm doubtful about that. 
She's asked if I would be "really mad."

I would appreciate any advice on this situation.

AITA for feeling this way? WIBTA for acting on these feelings? 


