Not necessarily. I mean, you don't have to be married to be in love. It's called making love for a reason. It's supposed to be with someone you love. But I don't think you should do it until you're old enough to have kids though.
Yes. I'm a Christian, so that's one reason. It's easier to avoid an STD too.
It's hard sometimes. They could have sex with you and leave, or it could somehow change things. It also shows you're more committed to the person you're with. :) I don't see the benefits of having sex before marriage.
Other than you get to pleasure yourself before you're fully ready to commit. Because marriage signifies commitment.