The Origin Story We Know:
As the leader of the supposedly peaceful (and yet always fighting someone) X-Men, Professor Charles Xavier's goals in life are simple: to protect mutants, to peacefully promote mutant rights and to help mutants and humans live together. He even founded Xavier's School for Gifted Youngsters to teach mutants to explore and control their powers, and definitely not to build his own personal mutant army. He's basically just an all-around awesome father-figure type to these kids, whom he loves.
But There Is Another Story ...
It turns out he kind of loves them a bit more than he should, at least in the case of Jean Grey.
The X-Men #3 (1964)
Yes, Professor, the only problem is the wheelchair.
Uh, yeah, so that's Professor X, easily in his 30s or 40s at the time, mentally admitting his complete and total love for his 15-year-old student Jean Grey way back in the third issue of X-Men. Not only is it super disturbing that this guy who leads and teaches kids on a daily basis was in love with his 15-year-old student, but it also means he's been in love with Jean basically every single moment of the X-Men's history.
So during every mission, briefing and training session the team's ever had, he's been making leadership decisions while secretly in love with one of his students and trying not to let it affect his judgment. And this has been going on for over 50 years, which is a terrifying amount of sexual repression, and he hasn't told a soul, except for Moira MacTaggert, the other woman he loves and can never be with.
Uncanny X-Men #101 (1976)
So, got a thing for redheads, Professor?