What are the essential factors constantly needed in a relationship to keep it alive.

If you are talking about an existing relationship that's circling the drain.... there's not much you can do. Let it fail, and move on.

If you're talking about keeping the heat on, remember what you did to get her. I think a guy needs to still court his ol lady - even if they've been together forever and have kids. Otherwise it has the potential turn into a couple of friends/roommates.

What are the essential factors constantly needed in a relationship to keep it alive.

Not too difficult...
Don't spend all your time together, keep doing things by yourself and/or with your own friends.

Be spontaneous, keep a sense of being adventurous instead of becoming a couch potato because you got him/her and are now in a perceived 'safe zone'.

You've got to keep things fresh and vibrant. Routine and ruts will eventually create boredom and kill romance and intimacy.

Work on good communication. No bottling things up, but communicate in a healthy clear way without any blame.

Surprise your partners with fun, sweet, cute things. Don't wait for his/her birthday or Christmas.

Compliment the other.

Make sure you spend enough quality time together.