No sex life

Advice/helpful tips on how to attract my man? Haven’t had sex in 3 weeks and before that we hadn’t had sex in over a month. He says it’s because he’s tired from work but he’s always going out with his friends & doing fun activities so I doubt it’s completely work. When I try to talk about how we never have sex he goes “that’s marriage. Our relationship is going to change”. I mean he isn’t wrong, but he doesn’t seem to interested in solving the issue either. I don’t really know what to do?