Welcome to the forums. I'm sorry you're hurting, and I understand the doubt. When I read your post, I almost felt you were answering your own question. You talk about the jealousy and resentment that occur EVERY time your partner plays with another. Those feeling are deep-seated, I know. Everyone in polyamory deals with this from time-to-time, but in your case they happen every time, and no amount of educating yourself or trying to talk yourself into polyamory seems to change those feelings.
That's why it seems, from my perspective, that you're really a monogamous person. At least, right now you are. People often change. I've read many posts from people who were monogamous for years before making a change to polyamory. Still others went in the opposite direction. Some went monogamy to polaymory to monogamy to polyamory, etc. The point is that we are not necessarily "wired" one way or the other (although there is still a lot of debate about this) but we go through periods when we are one way or the other.
If polyamory hurts this much, then you're not where you need to be to pursue it. You'll be happier with a person who wants you and only you. You'll feel better about yourself, and maybe down the road, when you've reached that place where your relationship is secure and you've worked on your own self-esteem issues, you can gently approach the idea with your partner.
I do wish you the best. Post often and let us know how it is going.