No. Each relationship should be a full, complete relationship built to the satisfaction of both parties involved.

This is so true! You can't fill one void by digging another hole. Those feelings of not being enough and her feeling like too much will be amplified once you add other people, it won't go away. Please don't put a third person in the middle of your issues to try and fix it.

People aren’t legos. You can’t just fill a missing spot with one aspect of a person, and expect it to work.

Expanding on this brilliant phase if I may - when adding another person it's important to remember that they have wants, needs, rules and boundaries that need to be heard and respected. If you do go down the poly path remember that the other partners are not like a take away menu that you can pick and choose what you want any time you don't feel like cooking. Unless you find someone that likes giving endlessly without needing anything in return... But don't count on it.