I'm not too experienced with sex, but I crossed that line with a friend and completely freaked out afterwards and distanced myself and he would NOT leave me alone.
I refrain from having sex simply because I don't get emotionally attached to the act, and would end up having a thousand partners if I went out all willy nilly and satisfied some hormones. Even after I lost my virginity, he was all hugging on me and I was like UGH, get away! Lol.