Welcome to our forum.
I'm sure you'll get things sorted out in due time, and Polyamory.com can help. Remember, just because X is polyamorous, doesn't mean you have to be, and the two of you can still be together, you just have to figure out if you can live with him seeing other people.
Anyway, read up on some of our various threads, and let us know if you have any thoughts, questions, or concerns.
Love means never having to say, "Put down that meat cleaver!"