How long before a therapist can have a relationship with his client/patient?

I'm writing a story about a 25 year old girl named Stephanie who slowly starts to fall for her 32 year old therapist Simon although he is getting married soon, he slowly starts to fall for her.

At first, she barely talks because her mother just died of breast cancer and she is trying to deal with the trauma and doesn't think he will be able to really help her but he slowly breaks through to her and along the way falls for her and she does with him.

So the reason why I'm asking this question is because I want to know how long after a therapist stops being the client's therapist can they be together?

I know he will lose his license if he acts on his feelings before not making her his client/patient anymore but I love reading forbidden love stories which is why I started writing it lol
How long before a therapist can have a relationship with his client/patient?
Post Opinion