My boyfriend doesn’t want to have sex with me

i would really appreciate some advice. Me and my partner have been together for almost 2 years and we are only having sex once a week at the moment because when ever we go to bed he always says he’s too tired. He used to always want to hve sex with me constantly, and this change has made my self esteem really low as i feel as though he doesn’t want me anymore. I feel like i’m going crazy feeling anxious about this all the time, no i don’t want us to break up i just don’t know how to make him want me.