I get lots of mail from women who are involved with married or otherwise attached men. They invariably ask how long they should wait for a guy to leave his wife or girlfriend before giving him the heave-ho.

My answer is always the same: Give the jerk the heave-ho now. Immediately!

Why any woman would date a man in the hopes that he will eventually leave a wife or girlfriend baffles me. Even if he makes good on his promise, this woman will snare a dubious prize: A creep who is capable of fleeing a relationship as soon as another female turns his head. She's netted herself a half-man.

In case you're dating a half-man and kidding yourself into believing his infidelity won't ever be your problem, ask yourself how you would like it if another woman snatched your man. If he's "snatchable," it means he's unable to commit fully to a relationship, and it will only be a matter of time before you wind up sharing him with someone else.

Women who date errant husbands and boyfriends are poaching other women's men. It's wrong. And, as your mother might have told you, wrong actions invariably lead to painful consequences.

If you have the bad fortune to be in this situation and choose to take your chances with Lover Boy, you can be relatively sure:

a) You'll wind up spending all your Christmases choking on Aunt Hilda's dry quiche and being subjected to Uncle Charlie's drooly denture readjustments (while, at the very same time in a Norman Rockwell scene across town, Lover Boy and his wife are joyfully beholding their children tearing open presents under their tree).

Or:

b) You'll wind up the jittery wife of a man who cut and run on his first wife and children. Trust me; if this scenario pans out, you will find yourself looking over your shoulder every day for the rest of your life. You'd have a much better time with Hilda and Charlie.

Is any guy worth it?

I didn't think so.

If you're stuck on a half-man, unstick yourself immediately. Stop taking his calls. Find another route home from work to avoid running into him. If you have to, get another job. Change your phone number. Give him the slip; your happiness and self-respect are at stake.

You deserve a whole man, so hold out for one. Raise your standards for a guy who's capable of loyalty and true love. He's out there. I promise.

Terry Hernon MacDonald is the author of "How to Attract and Marry the Man of Your Dreams." Sign up for free dating tips at http://www.marrysmart.com. Check out her blog at http://happygirlmusing.blogspot.com.