Not been having sex for months

Me and my partner haven’t had proper sex in 4 months. We’ve tried and he can’t keep it up. For context, we are in our twenties and been together over a year. He says he just isn’t interested in sex and isn’t turned on. This has obviously made me feel like shit and I feel ugly and very self conscious but he keeps saying I’m beautiful and it’s not me, it’s him. I just dunno what to do, sex isn’t everything I’m a relationship but intimacy is important. This is having an impact on our relationship and also on my mental health as it’s making me feel pretty rubbish.

Any tips?