It is a sin. If you're a committed follower of Jesus Christ, then do not have sex outside of marriage. If your boyfriend is pressuring you, stand up to him.
If it feels right, do it. There's really no rules to when you should/shouldn't have sex when you love someone.... It's like Muslims wearing head scarfs to 'follow there religion' when there's really no need for it all.
Although, I really regret the guy I lost mine to... You have to make sure hes right for you and that he's prooved himself!
As a Christain, I would say it is the best way, it saves you from so much pain. God wants us to be pure, without sexual sin before we get married. Sharing intimacy is very sacred, it not only bonds both parties involved physically, but emotionally as well. It comes with baggages if is is done outside of marriage e.g Heartbreak of past loves, sexual intercourse diseases, unwanted pregnancies et al. Well, the Bible is very strict about this, even Mary was a virgin and so was Sarah, Jacobs wife et al. In answer to your question, yes, if one is a true Christain, one must remain a virgin before marriage. Not only must one be a virgin, but one's thoughts must be pure as well, lustful tthoughts are a sin as well.