How to forget and clear things in my mind? I wish to get a peaceful mind again.
Well done for realizing things were not what you wanted from the relationship and for being brave and leaving it. This strength of character will absolutely help you to move on. It is regrettable that your first experience in a relationship was not a positive one.
Even though this relationship was not what you expected and was difficult to leave, it is ok to feel sad that it is over because I'm sure there were some good bits and it is human nature to focus on the good and minimize the not so good/bad.
You mention that towards the end of the relationship he threatened to isolate you from family and friends and I'm curious if that has happened. Are you spending time with family and friends who understand what you have been through and are supportive? Do you have interesting and engaging activities booked, things to look forward to?
When we feel sad it is easy to forget we are important to people in our lives and part of picking ourselves up and moving on is the process of self-care. This is often misinterpreted as self-indulgence, with lots of people discussing facials/face masks and such. However, self-care is initially about taking care of your basic needs; are you getting enough food & fluid, sleep, social interaction? Do you have working strategies for stopping your brain running overtime? Do you have any hobbies or interests that are so absorbing you don't realize what time it is? It may sound as if I am explaining the obvious and these are the things that get lost and missed when we are having a sad or depressive episode.
There is no fixed timeline for getting over a relationship, and one that you felt unsupported, or even scared in, can be more difficult. This can be because we are left with a feeling of injustice. I wonder how you would feel about writing him a letter and explaining how the relationship felt to you and has left you feeling. I must stress this letter is not for sending, this is purely for you to get your thoughts and feelings about the relationship out of your head. We process information differently when we read it to when we think it, so seeing how the relationship has made you feel may support you in finding ways to move on from it.
I hope this has been helpful.