Husband never wants sex but masturbates

My husband never wants to have sex with me soon after we got married (been 4 years). We pretty much have a sexless marriage for the last 3 years (a few times a year at best and most of these times I’m the one initiating). It got to a point where I stopped initiating because I was constantly feeling rejected and it affected my self esteem. I’m open to trying different things in the bedroom, open to wearing lingerie I stopped wearing them when I was being rejected no matter how I looked and open to pleasing him in different ways (he doesn’t even like blow jobs or any form of oral sex). I realise now that his understanding of sex is pretty much from pornography.

I’ve raised this issue many times with him but nothing changes. He comes up with excuses like being tired, stressed etc. and I fully sympathised with him and even considered he has some sort of medical condition until I found out he masturbates regularly, follows naked women on Insta and watches porn (he didn’t deny it). I stupidly thought he can’t be masturbating that much when he never wants sex. I brought it up with him yesterday and told him I don’t want to go on like this. He apologised and said it’s nothing to do with me and that he’s going to try to change (he said that a few months ago and we only had sex once). He unfollowed the naked influencers on Insta. He can’t answer why he masturbates and doesn’t want to have sex with me. He just says he doesn’t know. I assume it’s porn addiction causing this. I wouldn’t have married him if I realised this was a problem. I need help trying to understand why a straight man doesn’t want to have sex with his wife who’s willing to give it all but doesn’t stop jerking off. I’m completely heartbroken and don’t want to continue our marriage like this. We’re in our late 20s so there’s many decades ahead. Send help!