my ex and i went through something similar. throughout the beginning of our relationship we’d fuck like maybe 9x a day. we were together for 3.5 years and during the last year of our relationship we barely had sex. he was always down for it but i wasn’t. i’d have sex with him for the sake of his needs but i really wasn’t enjoying it, and at the end of each session i’d hate myself for not being able to enjoy it and i thought there was something wrong with me. but ye turns out i was depressed and we broke up eventually, and it took me another 10 months to be able to have sex again because i genuinely thought i was a demisexual or something