Am I entitled to not forgive someone who caused me psychological harm, knowing that I sinned in my relationship with them?

One must stay away from relationships between young men and women through modern communication means and otherwise, due to their bad consequences and great harms. You have done well by cutting off your relationship with this young man and repenting for what has passed. You have no right over him such that you would not forgive him. It is better to close this door and occupy yourself with what benefits you in your religion and your worldly life, and ask Allah to grant you a righteous husband.