I have a low sex drive

Within the last 9 months I haven’t been very sexually active with my fiancé. We moved in together last year in June. He always wants to have sex. It doesn’t matter where or when, but for some reason I’m just not in the mood or not very interested. Whenever he asks to have sex I’ll say “maybe later” and it usually never happens later. I just really don’t feel like having sex. Now he’s upset because he feels like he’s constantly getting turned down and he shouldn’t feel this way toward his fiancé. I love him very much. We’ve been together for 3 years. He makes me happy & he’s amazing. I feel bad that he feels this way. I’m thinking about just saying yes to sex more often just to make him happy; whether I feel like it or not.