I don’t think it’s your job to fix things in this instance.
It’s his problem, he likes it, he doesn’t respect you, he’s messing with your head deliberately.
You can’t make another person do what they don’t want to do.
I’m no expert in relationships. But if I call DP he answers straight away 50% of the time. The other 50% he’s working and can’t answer, or he didn’t hear the phone because he had some shit on YouTube blaring in the background. So when he sees the missed call, he calls right back and goes: soz, didn’t hear it, I’m watching xyz whilst ironing. And I go: no problem, I wanted to ask/talk about whatever.
He always texts me good night when we’re not together. If I don’t answer, he knows I’m fast asleep, he’ll wake up to a kiss emoji. He knows I’m just asleep, I’m not ghosting him.
He doesn’t think I’m a cheeky cow if I can’t hear the dog wanting to go out, he knows I’m shattered, he gets up, takes the dog out, he’s confident I’m not just pulling a fast one.
I went drinking with some colleagues after work last week. He called me on his way back home to ask if I’ve eaten. I asked him to swing by and pick me up on his way home, came by, said hello to my last standing colleague (a man), offered him a lift home, never met the man before, he didn’t ask: who was that, why was it just the two of you.
I think that’s pretty secure.