If you avoid all the many bad endings, then you prevail against the games villain and get the following choice:
1. Marry the princess and become king. (this unlocks an extended sex scene, so you'll want to save and choose this option even if you don't want this ending).
2. Decline the offer of kingship and settle down with one of game's other characters (your choices are limited to those characters who you've romanced already in the game).
3. Like 2, but you're settling down with two characters as part of a trio (again, you have to have advanced your relationship with them properly during the game proper)
4. Don't partner with anyone and continue enjoying your bachelorhood.
Once you make the choice, and see the scene if you chose kingship, there's an epilogue that tells how each character fares. If you romanced a character but dumped her to marry someone else, she will be sad and tearful as she goes on with her life without you.