How strong is the assumption that men are only after one thing?

Yep. I assume it. I guess it may not be true for all guys, but I've even heard from guys that all they want is sex and even if they don't ask for it, it's what they're thinking about. I even worry about it with my boyfriend, that all he wants is me for my body (we haven't had sex and I wont until I'm married) and once he gets bored with waiting and just being able to kiss me, he'll move on.