@thisprimarycolour
One reason that a person can be in the wrong relationship is that any relationship is wrong for them, because they haven't got their head around how they feel about a previous relationship. If you're not capable of trusting your partner, whether it's because they're not trustworthy, or because you erroneously feel that they're not trustworthy, then, at the very least, you should be able to have a conversation about it. Can you do that with him?
Hard to know what's acceptable anymore
It's not something that's supposed to be 'externally verified'. You decide what's ok for you. Everyone has different levels. You will be ok with stuff that someone else wouldn't be, and vice versa.
The only important thing is that if you're not happy with what he's doing, whether it's looking at porn or eating yoghurts, you can have a conversation together about it with the aim of finding a compromise that works for you both.
It's hard to trust someone when you think that things you might hate are 'allowed' by some external set of rules. It's not the case (until you get to legal issues) Every adult is allowed to decide for themselves how to 'do life'. Each of us is responsible for our own feelings, and so, responsible for making sure that the things we do and the people we spend our time with are ones that make us feel happy, safe, secure. If you choose people with whom you feel insecure, you are essentially saying 'I'm welcoming more time feeling insecure into my life'.
Don't try to adjust your feelings to a set of rules. Change your people, so that the people you spend your time with are the ones that make your life feel good, according to your rules. Let your emotions lead the way. Follow the emotion of 'happy'.