We can all learn to forgive and to accept forgiveness. It might take long before these traits become second nature, but the process is worth undertaking.
I do have regrets in my life. But I have also practiced focussing my energy on making peace with what I can't change. The past that I can't control doesn't serve me now beyond being a lesson.
Happiness is a choice I decided to make intentionally, regardless of the ups and downs I encountered. At some point in my life, it became clear that I could not base my happiness on people, things or circumstances, all of which are unpredictable and ever-changing.