There are Apple instructions here on how to create a hidden album which you can access from the phone or mac
With Photos, you can control which photos and videos are visible and what's hidden.
support.apple.com
There are also apps that will do this for you although I haven't tested them. There's one I know looks like a calculator and you tap a code on it to unlock the hidden pics. I'm sure a search will give you that info if you want to go down that route.
I do get it. It's no different really from pictures of your male friends from earlier in your life and as you say, they are part of your life and part of your memories and there's no reason they should mean anything more than that.
I advise you to be a bit careful though because if your other half discovers you've hidden photos it'll look way more suspicious and get you into far more trouble.
I'd be more tempted to go down the tried and tested bureaucracy route: put them in a wrongly labelled folder and hide them in a load of junk.
Good luck