IT is really simple:
Have a healthy relationship with yourself, first.
Have a plan for the type of relationship you want. Dont settle for less.
Get to know someone BEFORE you sleep with them, unless you just want casual sex with no expectations.
People expect sex to equal intimacy. Sex isn't intimacy - intimacy is being able to be completely honest and yourself with someone - even the jagged bits.
If you feel uncomfortable or mistrusting - It isn't YOU!!! I have never worked with anyone who has had that gut feeling that something isn't right, where they have been wrong.
Trust your intuition - it won't let you down. Ignore your instincts at your own peril, they may come back to bite you later.