It’s routine protocol, I’m afraid.
Your version of events is that a student at the school (irrelevant that you say he’s an adult - even if he’s 18, he’s still regarded as a young person for whom the school has safeguarding responsibility) has behaved inappropriately towards you, that this behaviour constitutes harassment & that you’ve reported it.
Have you logged this on the school safeguarding system - CPOMS or similar?
It seems the student has reported your interactions differently.
Obviously, this is difficult for you, but yes, the school has to suspend you whilst they investigate. In this situation, you’re an adult who MAY be a risk to your teenage students.
It’s an occupational hazard.
As for what the school is doing about the student’s behaviour, you’re currently the last person they can discuss it with, given there’s an open complaint BY said student against you.
You need to sit tight on this one, & contact your union. Report to school if this young man OR any other student attempt to contact you. Check your social media is locked down.