TL;DR: This is a little long and mostly abstract. You can skip to the questions in bold further down.

I have been in a poly relationship for 8 months. I deeply believe in poly and I don't think I'll ever be monogamous again. This very relationship has brought a great deal of happiness into my life.
One of the things I love about poly is that it makes you think. You just can't apply centuries old patterns to your relationships : you have to be creative and look inward and question the ethics of your actions, and then make decisions about what to do next.
The most challenging thing I learned is that fear, discomfort, jealousy and sadness can happen, but that doesn't mean it's the end of the world. You can acknowledge the feelings and let them go, you can discuss them, confide into your partners for support...
But, right now, I'm wondering if I let this go too far. For a few months now, I often get feelings and thoughts such as:
"is this OK ? I should be OK with this, right ?" or
"I don't like that at all but I can't wrap my head around why",
"he didn't do anything to me, why does it feel so bad then ?",
"I believe that he would chose himself and his own pleasure over anyone else's comfort" - more precisely: "if he's getting what he wants, he doesn't question his actions' consequences on others beforehand"
and most recently "can I trust him ?".
(To be fair: he's not violent, not unethical (except for little white lies here and there), he listens well and always offers support, he's understanding and loving.)
I eventually chalk it up to "the normal discomforts of poly" and fall back into a nice, very pleasurable relationship where everything goes quite well. But then something else comes up, and the cycle starts again.

Now for my question. Does any of you feel the same ? Are (poly) relationships prone to these types of questions ? Do they endlessly come back ? Am I just neurotic/a worrier ?

Sorry I'm not giving details. I'm trying to just know what your experiences with doubt in poly relationships are. If this doesn't speak to anyone I'll post something more precise, but I'm having a hard time pointing out what really bothers me and making it into a readable post.