Lasting relationships develop when two people are equally yoked spiritually, emotionally, intellectually, and physically. --Jason Illian

It's Not About You
Love is selfless. You have to put the other person's best interest first if you want a healthy relationship.

Self-preservation
Guard you heart, guard your body.
Emotional and physical chastity is crucial in a healthy relationship.
If the other person is pushing you to put out or give in he/she is not keeping your best interest in mind and is making it about them, not you.

Communicate
In general, you should be able to talk to each other about almost anything, like good friends. If there's a problem, you need to be able to talk about that too in a mature, rational matter.