Sometimes, the guy wants to be with you regardless.
When you are in a situation where the guy is in it just for the chase, it wouldn't matter if you give it up before or after you get into a relationship, he will end up walking away after you have sex.
If he really likes you, he will like you both before and after you have sex.
I was unofficial with a guy for 4 months and we had sex. It ended on a nice note (I walked away). I knew a girl that got into a relationship, gave her virginity to the guy after dating for 2 months and he broke up with her/stopped calling her the day after.
Its all subject to change.
Personally, I say go with your own schedule. If you feel like the guy is in it for the long haul and you are comfortable then go for it. If you feel like he is in it for the chase/sex regardless of being in a relationship or not (ie: you have doubts about him), then it doesn't matter if you wait to give it up or not because he was probably not serious to begin with.
Edit: I would also like to say that you become a f**k buddy the moment the only time he calls/wants to hang out with you is if the two of you are going to have sex. He won't call to ask how you are doing or try to hang out with you in a non-sexual way. Avoid that situation at all costs.