Afterwards, I always dreaded the awkward next encounter. It is typically the woman who tries to impose the "friends first" limitation on the man, when what she really means is there's not going to be any sex (aka "going slow", aka "down boy, down!
It's important to treat all your friendships with respect. ") because she seems to think the most salient aspect of friendship is not having sex, or maybe because she wants traditional courtship and/or thinks the man has to prove himself to her first (rarely is it the other way around) but can't put it that way.
Jealousy and possessiveness occur in all relationships- including friendships.
I've been envious of new friends that supplant old friendships.
I've never been "friends first" with a boy, though the concept is quite fascinating. Many experts advise that couples should be friends first.