He was her mentor when she was 16. Ffs why would you defend such gross behavior. It wasn’t like he met her at an award ceremony at 16 and then at a coffee shop 3 yrs later and they hit it off. (Still creepy but not gross) He’s been a relevant part of her life from 16 on.
Because there was no "gross behavior,"--there is no proof they had sex, or he met her with the intent to have sex. They met, period-- it looks like it originally was a mentor/student relationship, and there is no proof otherwise. Your mind immediately went into "OMG it must be sexual!" without any proof of such.
Until you can proof he wanted to have underage sex with her, your argument fails.