Do you ever look at anyone else’s boobs (or any other body part for that matter) and think they are disgusting? Or that they should be embarrassed or ashamed of their body?
I would recommend therapy as it’s clearly a very deep insecurity and you deserve to feel comfortable and confident in your own body.
I would also recommend following body acceptance pages online, I like @ lydiareeves_artist on insta, she is an artist who has dozens of casts of normal people’s breasts and bodies on her page, they’re gorgeous and will show you that boobs come in all shapes and sizes and all are beautiful.
I promise you that you are not disgusting and your boobs are really not that different to anyone else’s. If your boyfriend was that desperately shallow and superficial that he would actually leave you for literally no other reason than just a glimpse of your boobs then you’d be dodging a major bullet, you don’t want anyone that sad and immature in your life anyway. You are a lot more than just your physical appearance and his love and support for you is not just based on what you look like.