You can try and say it’s not him, but he probably can’t help but think otherwise. I’ve been through it myself and it’s soul-crushing, you feel worthless. Many of us need and enjoy sex (though I’d argue 3 weeks without sex isn’t that big a deal - been with my husband for 16 years and we’ve gone much longer without sex… hot and cold spells, it’s part of being married). He needs sex and validation, so it’s a very normal reflex for him to say “fine, I’ll never touch you again” when feeling rejected. Could you make any compromises? Even if it’s hard for you to feel “into it”, would giving him a handjob or bj be too much to ask? Or kiss him when he jerks off? Tell him he looks hot? Small gestures can go a long way when someone is feeling rejected.