Boyfriend doesn’t want sex

Me and my boyfriend have been together for about a 3 years and use to have an awesome sex life. The past 6-8 months I feel like no matter I do he turns me down at the idea of sex. We have talked about it being an issue and how it makes me feel sad and he always claims it’s not me he’s just not in the mood or too tired too stressed ect. Even when it’s not even sex just simple things like making out or touching it just feels like I’m constantly being pushed away. I know sex isn’t the most important part of the relationship but once a month isn’t working for me anymore. Tips or advice on this?