The issue is that you're an adult, unless you're assessed not to have capacity to make your own decisions vulnerable or not you're considered responsible for your choices including your decision to keep seeing an abusive T.

So, had you said no, objected to being held or to physical contact and and you complained and not gone back you could argue lack of consent, if you were under 18 you could argue breach of trust and it would be an offence. If you, as an adult with agency over your own decisions allow a T to hold you and touch you, keep choosing to go back and make no complaint about it at the time I could see the police struggling to prove an offence.

I'm not saying he didn't harm you, you know my views on that but I can see why the police might struggle to find evidence that you were groomed or that you didn't have the choice to leave at any time. I'm guessing that some of the correspondence you've sent your T would point to you wanting therapy to continue so he can evidence you were there by choice.

Sexual assault is actually the only criminal offence he may have committed, because vulnerable or not, you chose to keep seeing him.