I came to realize something while I was single:

Only date someone who doesn't need you.

That's right, find someone who could be perfectly content without you, but wants you in their life. Otherwise you run the risk of being a walking ATM, a surrogate parent (for your partner and/or their kids if they have them), or, worst of all - the emotional crutch.

When you find someone who doesn't actually need you, there's plenty of material for a synergistic amplification that benefits you both. Otherwise, often times, instead of a beneficial relationship one of you is going to be dragging an anchor.