How do I forgive myself for acting out of character when I was 18 and I chased my toxic ex who cheated and lied to me. I feel shame and guilt?

How do I forgive myself for acting out of character when I was 18 and I chased my toxic ex who was hot and cold. I begged, chased and cried to keep the relationship and now I’m 27 but and have strong self worth but I’m haunted by my past actions and feel shame and guilt. My past behaviour was extreme and I even waited outside his house for hours. He was 24 at the time and he cheated, lied, spat at me, and kicked me when I tried to get chase and beg him.
How do I forgive myself for acting out of character when I was 18 and I chased my toxic ex who cheated and lied to me. I feel shame and guilt?
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