What happens "the morning after" depends a lot on what happens the night before. 

If you and your partner talk about the decision to have sex, expect similar things from your experience together, and practice safer sex (like condoms and birth control), you'll probably feel pretty good "the morning after."

Sex won't automatically bring you closer.  But you'll feel better if you and your partner agree on some important stuff.  Why do you want to have sex?  Are you just fooling around? Or is this love and commitment? Do you and your partner want the same things from the relationship?  This is real important.  If you want different things—casual sex vs. a commitment—you could be in for trouble. 

Also remember to talk abut the consequences—pregnancy, sexually transmitted diseases, HIV/AIDS—and how you would handle it. And remember the contraception if you are in a heterosexual relationship.