Actually sexualization- as opposed to attraction- to breasts isn't natural, which is wild. There are plenty of cultures where breasts aren't sexualized, especially near the equator in some traditional cultures where women go topless.
Also as a lesbian in the US who definitely has internalized sexualizing boobs, I don't find it at all distracting when someone isn't wearing a bra. Maybe it is just that I see boobs in non-sexual contexts so it only is sexualized within a sexual context? That might be useful if you're interested in unlearning this habit.
It isn't that hard though. Go to a nudist retreat or beach, practice figure drawing (there are plenty of free online figure drawing resources), look at medical indexes, watch medical documentaries, just off the top of my head.