"More so, I don't want to come out of this regretting it. I don't want to come out feeling used and manipulated... I don't want that."
I really like what you said here, Mookitten.
Ug. Tough situation.
I agree with the folks who have posted here about your partner seeming pretty clueless/hard-hearted/whatever in his attitude toward you. And from what little I know (I'm new to polyamory, too), poly isn't about just one person doing anything he/she wants while the other watches and weeps.
For what it's worth, I'm the poly one in a poly/mono duo--I'm a bi female with two significant men in my life. I'm brand new to this scene, and am constantly monitoring my relationship with my primary partner, making sure he's okay if I'm with the other man, honoring any plans we already made, etc. If my relationship with the other man evolves to a similar place, I plan to be as open and concerned with him. At the moment, it's pretty overwhelming and difficult; I hope it gets easier with time and mileage.
Here's what I would do if I were you:
1. I would try to focus as much attention as I could on the good stuff. Obviously, there is good stuff going on as well as bad stuff, otherwise you wouldn't think twice about shaking the dust from your feet and moving on. So at least 55% of the time, focus on what you LIKE and LOVE about your partner and your relationship. AND focus on what you WANT, not what you DON'T want. If you want a monogamous relationship with someone who adores you--plus all the goodies you have in your current relationship--then eventually either the universe will cause your current partner to have a change of heart and come into line with what you want, or it will move him out of your life and leave room for your dream partner to move in.
2. Don't make any big changes in your situation until you feel better. Remember, you're going to be taking YOU with you into any situation, new or old, so feeling good about YOU is paramount. And if you focus on the bad stuff in any situation, you're going to be taking THAT with you into the next situation.
Sorry about the mini-novel. That's my $1.50, as awkwardly stated as it is. I wish you the very best.