Is it cheating if you haven't defined the relationship yet?

Anonymous
My first question is did sleeping with T count as cheating even though M and I were not defined? I have no idea if M was still seeing other people between the time that we first started seeing each other and the time that he asked to be exclusive. My second question is, should I tell M that I slept with T before we became officially exclusive? And is it necessary for me to tell M?
I am currently in a steady relationship with an amazing guy who I started seeing the first week of October. Unfortunately, I did something that I am not proud of, and it's been eating at me for months. So my current boyfriend, M, first started seeing each other early in October. A few weeks later I spent the night and we had sex. When I tried to define the relationship M called me his "not girlfriend" and said it was too soon to be exclusive and he didn't want to define us yet.
A week later a guy who I had previously been on 1 date before, T, reached out to me. I hadn't heard from him in weeks before I started seeing M. Long story short I ended up having a one night stand with T the night after Halloween. The following week M decided he wanted to be exclusive and we officially defined our relationship.
Is it cheating if you haven't defined the relationship yet?
15 Opinion