This is only my experience, so take what follows for what it’s worth (not much).
I have been in the same situation as your partner (though I had sex with my partner more ofte, but still way less than before medication).
Simply put, I was ashamed of my low libido and not in a good headspace even with my medication( which was supposed to help).
I was so ashamed that I didn’t want to initiate sex with my partner. It was not rational, but that is how I felt at the time. And I would sometime watch porn so that I could get the dopamine I would get from sex, without the shame.
I know it won’t make you feel better, but hopefully you can have a different perspective on how your partner might feel and get, hopefully, a new track to find a solution to your problems.
Also, there are some medications that can help with libido (Wellbutrin if I remember correctly). Might be worth it for your partner to check with his doctor.
Worst is that some medication will kill your orgasm. So you get your libido back, but you don’t get to enjoy your orgasm anymore.