OK. Thanks for answering.
At the moment, those things are habits and habits can be broken. If you find yourself peeking or wanting to peek at his phone - stop yourself. Move to a different room or do something completely different to break the pattern. The less you do it, the less you will want to do it.
Take someone who habitually checks their partners phone (I know you've not said thats what you're doing but hear me out). They look but don't find anything. Great. But they start to wonder if their partner is hiding or deleting messages (so the thinking and possibly behaviour escalates) or they tell themselves that it doesn't matter that they're looking because they never see anything anyway. But all the time they're doing that, it reinforces the idea that its necessary.
And that escalation looks like thinking what if they are hiding or deleting messages? What if the one time they don't check the phone is the time they would have found something? So it becomes an ingrained behaviour. That's the behaviour that's reinforced and rewarded by feeling reassured.
If they stopped checking the phone, took responsibility for their feelings and actions and just rose above it, then that is the behaviour that would become reinforced instead.
Whilst peeking isn't the crime of the century, what happens if 'peeking' over his shoulder no longer feels enough? What if you decide that looking through his phone is justified. Just this once..?
You say you question your partner about these women. Reflect on the nature of these. Do you ask how he knows her? Whether or not he thinks she's attractive? Whatever it is, ask yourself how much, if at all, it actually matters.
Eg does it really matter if he once dated her? Does it matter if she's the best friend of an ex he kept in touch with? Does it matter if he thinks she's attractive? Would you want to hear an honest answer? What if it was hurtful? Do you want him to lie to make you feel better? What's the point in that?
What reassurance does the questioning give you? How can you offer that to yourself instead?
The trick is to be really logical.
You can't control what happens in the future. Whether he finds someone else attractive or whether he falls in love with someone else. All you can do is trust what he says (if he's trustworthy) and hope that he continues to choose you for as long as you choose him. And make sure that you invest in yourself socially, professionally and financially so that if your worst fears come true, you'll be OK.
The difference between people who worry and are dominated by feelings of jealousy and those who aren't is that they accept they have no control over the other person but also that they will be OK if it all goes wrong.
My exh said to me when we were still together that he trusted me not to cheat on him because he knew I was better than that but that, if I did, it would say a lot more about me than it did him. He was right. And the reverse was true when he did eventually cheat on me 😉
I'm sorry if that's a bit muddled but I hope you get what I'm saying.