Feeling like you were cheated on is perfectly apt if you had rules and they were broken. What is "cheating" if not breaking the rules? Poly relationships just come with different rules than mono ones. Sometimes there are practically no rules at all beyond safe sex, sometimes things are much more rigid. Many people find that they need rules at first to feel safe, but that the more flexible they're able to become the smoother things seem to go.
I would very strongly advise against feeling like you need someone to love you equally (though it seems like you're already moving in the direction off letting that go). It's a common dream, and not a realistic one. It does happen to some people sometimes but it's very rare and if you hold that expectation/rule you'll just put a lot of pressure on everyone and run into a lot of heartbreak.
People are just too individual and love is just too serendipitous for it to be sane to expect it develop with Partner A just because it develops with Partner B. A "vee" is the name we give a relationship where one person is dating two people who are not dating each other. See my sig line for an example of a particularly close vee -- my gf Gia is the "hinge" and Eric and I are the "wings" -- though technically, since I'm dating Davis it's an "N" now if we draw him his own separate line... but let's not get too complicated.
Start dating separately, and expect to get a vee or an N, and if a triad happens you can be pleasantly surprised.
Friendship is not too much to hope for, and many poly people do consider friendship between metamours to be a crucial part of what keeps everything running smoothly. Sometimes it all clicks right away, and sometimes these friendships take a little while to form because jealousy or nervousness get in the way but eventually become very, very strong. But again, you can only expect so much -- if you don't end up being bosom buddies with your partner's partner, this doesn't mean that anyone has done anything wrong, these things can just be hard to control/predict. A strong basis of respect is non-negotiable on the other hand.