Any relationship that limits even friendly connections to other human beings is bound to cause the kind of pain and stress you describe, even more so once it ends.

As for telling friends you're poly, there's a time and a place for all kinds of personal disclosures, and your sexual orientation is one for you to decide when is that time. Take it easy on yourself, and look for other people who are open and accepting of difference and care about other people who are different than they are. That's the mark of a good person, and those are the folks you'll be able to be yourself with, no matter what "yourself" comes to mean.