21-year-old female, what should I do about this 34-year-old male?

I met my ex in April and moved in with him in May. He was incredibly sweet, always showering me with gifts and never showing any signs of toxicity. However, we broke up in June, and I moved out. In September, I ran into him at a place I often go to, and three of his friends mentioned he had a girlfriend. That evening, he approached me and started a conversation. I asked him, “Don’t you have a girlfriend? You should focus on her, not me.” He insisted he was single and invited me to talk privately. When we arrived at his apartment, I discovered his girlfriend was there, and upon seeing me, she decided to leave. In an unsettling turn of events, he grabbed her arm and yelled at her, showing signs of physical abuse, which I witnessed and heard. Afterward, I urged her to break away from him, and she did. Unfortunately, following that incident, he began to stalk me, as his friends informed me, and I noticed it myself. We stopped communicating in November when I had to go to the hospital for a couple of weeks. We haven’t spoken since before my hospital stay, but lately, I’ve found myself missing him and reminiscing about the good times we shared. Now, I'm considering reaching out to him but I need some advice on what to do. What should I make of this situation?