Was I wrong to show up unannounced at my girlfriend's house?

One night I was at a niece's birthday party. I noticed my girlfriend had gone MIA with texting. I thought nothing of it so I went for a night run after the party. I got a strange feeling on the way home so I decided to drop by her house. I found her co-worker walking her to her house. i pulled up right as they kissed each other. She always said it was wrong that I dropped by that night. That it was creepy and since then was afraid I would show up randomly. Like WTF? Seriously? We were dating each other but were not boyfriend and girlfriend at the time. We had broken up but were still hanging out as usual. I still felt betrayed. Am I wrong to have felt that way? Wrong to have shown up?
Was I wrong to show up unannounced at my girlfriend's house?
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