Lots of things going on here. Your reduced libido could be something that is naturally occurring due to stress or lifestage, or it could be medication-related. Are you taking medicinal birth control? Any other medications?

Is there anything about your boyfriend that you just can't stand, bad breath, body odor, or something you don't like about the way he touches you that you have a hard time telling him, or you've told him and he hasn't addressed it? Or, even if he's your 'best friend' are you turned off by something else that has developed, for example, is he meeting your needs in terms of household division of labor, do you feel noticed and appreciated?

He wants to feel attractive, so your rejection has caused him to pull away, and be more defensive. You seem to be on edge, and you're not getting the physical and emotional closeness you want because you don't want it to lead to (bad) sex.

Not sure whether you can solve this on your own, or whether you need outside help.

Maybe you can agree that most nights of the week sex is off the table, and you go to bed together and just talk, cuddle, rub each other's backs and express your support and appreciation without it leading to sex, so you both can relax in the knowledge there will be no disappointment. Maybe some nights you can get him off without having sex, or he can do that for you. Maybe agree that you'll try sex on a specific night, after you've had some time to reestablish closeness and trust, and with the agreement that you can say No at any time if it's hurting you, and that he can't take it personally while you're working through this.