Is he willing to watch you masturbate? Is that a thing that could help ease him into it? I do personally find quite a difference between masturbating while being full-on watched by my partner and us masturbating together. Being just watched makes me too conscious of my self and takes me out of the right mindset, and that might be what he feels. So maybe he'd be more willing to 'give himself a hand' while you're watching if you were also not paying super close attention because you're busy pleasuring yourself.

My partner and I haven't done PIV in ages, at one point several years in, I flat out told him I wasn't having any "sex" anymore where I didn't get at least a good fighting chance of orgasming, and that meant I'd have to do it myself, and he could either adjust, evolve, and join me, or he could pout and be bitter by his lonesome. We pretty much do the BDSM type play stuff for a while, pulling stuff from our trunk of sexy-time paraphernalia, until we're both all worked up and then one of says "let's go lay down" the other is like hell yeah, and then we dive into getting ourselves off in the ways that work best for us. He has a bunch of whirring devices going, and I have a simple tea towel that I rub my clit against. We both agree it's the most satisfying "sex" of our lives, and we're both old sluts so we've had lots to compare against.