I kissed someone when my ex and I were considering getting back together. Am I a terrible person?

My ex and I broke up a little while ago. We started communicating again about a month and a half after the breakup, and then started hanging out. Things started to feel like we were dating again and he actually brought up the idea of getting back together. I was a senior in high school (who was moving far for college) and he was a freshman in college (who attended a local college). When I eventually told him I was also interested in getting back together, he was happy but wanted to make sure that things would be right before he made things official. Fair enough. However, months passed and I had been nothing but healthy, supportive and reassuring, but he was still very stuck in the past. We both heavily communicated about this but things still felt a little stuck.. despite this we were still very happy. In the last month of our “situationship”, he was intoxicated and we got into an argument in which he was very aggressive towards me. We had combated multiple arguments before and came out strong but this one was different. This led to a month of him acting incredibly strange, little to no affection, conversation, effort, etc. (and anything else you can think of). I repeatedly told him I was unhappy and concerned, especially since my move out day was quickly approaching, but things didn’t improve. I was so unhappy because this was such a drastic change but every time i brought it up I was told “everything was fine and will get better soon”. Nothing changed despite my begging. He also missed my 18th birthday and grad party in this month period. So how was I supposed to believe him? I, impulsively, kissed someone else because he was giving me the attention I was begging for. I told my ex and we mutually agreed to go our separate ways. What I did was wrong.. I am consumed with guilt. But am I awful? I never EVER want to hurt him… I take full responsibility for what I did and there is no excuse.. it was so immature.. I was just so sad.
I kissed someone when my ex and I were considering getting back together. Am I a terrible person?
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