Mother died, her (unmarried) partner is refusing to give me any of her belongings

Location: Michigan, US.
My mother died suddenly last year, and though she lived with her boyfriend, I (next of kin) ended up as her sole executor as she had no will. Her boyfriend has been… difficult throughout this process. Barely speaks to me, won’t answer my calls/texts/emails, the rare times he does respond he’s pissed and explodes with anger, and won’t say why. I can barely converse with this man.

The main trouble is, since they lived together, literally all of my mother’s possessions are in his house. Her name was never on the house, she moved in with him a few years ago. I haven’t been allowed in the house or to go through any of her things. I’m told that her possessions, at least those which I can identify/describe, legally belong to me as her executor. I don’t want to take everything from him. He is not a nice man and frankly we’ve only ever put up with each other for my mother’s sake. But I know this is devastating to him too. Nobody expected her to go so suddenly. I have no desire to clean out everything she had from his house, but there are certain, very specific items of hers which mean a lot to me that I would like to have.

After well over a year, I have finally gotten him to start talking to me a little, and gave him a list of items of hers which I desire. He confirmed he has all of it but is refusing to give any of them to me, instead saying he “promises he’ll make sure they get to me when he doesn’t need them anymore.” I strongly feel like it’s just an attempt to blow me off and hope I forget about it eventually. I’m torn on how to handle him at this point. I want to just be done with the stress this is causing me, and somehow get him to commit in (legally-provable) writing that he will give these items to me in a certain timeframe. How would I even go about this? Given how difficult it is to get him to talk to me, I feel like a template he can fill out & email back would be easiest, but idk how admissible in court that would be, if it ends up coming to that.

Or, might it be better to simply lawyer up and demand these things now? I’m afraid to even mention the word ‘lawyer’ to him, lest he suddenly “misplace” these items that mean so much to me. It would not be the first time he’s done something like that.

Are her things truly legally my property, given the circumstances ? How should I handle trying to get these things from him?