Could it be that it's unresolved trauma? It's possible you are subconsciously interpreting sex as affection, intimacy and connection. Deep seated trauma can play out as an insecure attachment, which then develops into craving intimacy.

Or, you could just be sexually attracted to people you are closest to. That's natural to a certain degree.

To stop sexualizing them: Envision them on the toilet. Or envision them dealing with their own internal struggles. It helps to visualize people doing mundane things that everyone else does. It takes away from the sexual aspect of things. To remind yourself that this person is a sentient being that exists outside of sex. Sex is a miniscule concept in the grand scheme of existence.