So I've had 2 offers to be fwb from 2 different guys?

But I'm not into that, I kinda have this idea that one day I'm going to find Mr. Right and I don't want to **** around with some guy just to have a good time now, and take away from Mr. Right. I kinda even want to wait til marriage. But my question is why do guys want to be my FWB but I can't get a guy into a relationship?