How can I go back to being a good person?

All of my life, I had people fuck me over and take advantage of my kindness, so I decided to stop caring. One of my ex-friends kept coming back for the past 5 years to fuck me over... I've now got My get back, and she's afraid to leave her house. I didn't do anything physically to her, just mental stuff through social media. Another ex of mine made me lose my kids, so now I made sure she was homeless. As of last, she's been blowing up my phone, crying with nowhere to go, sleeps in her car. I feel heartless I don't care at all that I hurt them. How can I go back to my old self?
How can I go back to being a good person?
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