100% do not disagree with you - just trying to relay the facts and law of the situation. Did a little research and spoke to a close friend who works in Title IX compliance.
Here's the answer: Title IX provides a blanket ban on a coach dating a student-athlete or employee in athletic office (makes sense), but not coach/professor dating *any* student (that's case-by-case and primarily looks at power imbalance). Schools are free of course to have their own code of conduct/policies on such situations. OU has a policy that prohibits dating where there [paraphrasing] is a significant power imbalance. If you think about it, it makes sense - "want to be the highest-paid employee at this school, cool, but you can't date students" isn't a terrible trade-off. That's what Smith likely is being charged with violating and given that he's going through an ugly divorce, I'd imagine that it's his wife who brought it to the school's attention as she's planning on using it against him in the divorce. As in, heads up, we're filing for divorce and there is a lot of salacious stuff in here that's going to make Smith look bad (texts, emails, pics, stories about them getting down in the football office or something) and by proxy OU look bad.
Again, don't kill the messenger. It does suck for Smith (and moreso the OU program and diehard fans like you) but at the same time he certainly knew he was violating the OU code of conduct. And the timing particularly sucks, what with bowl season coming. Moreover, my friend said you'd be shocked at how much situations like this rock a school internally - there will be a Title IX investigation that will sweep in a lot of coaches and maybe players and takes months - so a lot of schools have policies that say you can't do it because it's not worth the trouble to the administration. My friend's exact words "I wish I worked there. The coach is getting railed by title IX right now."