The only person you've cheated on here is yourself. Which doesn't exactly make it simple but- it's easier to tackle. When you sit down and think 'why did I do this when I feel another way', the only one holding you accountable? Is you.

[ Again, doesn't make it black and white but- does pare down the variables to something manageable. ]

First thing to figure out that involves anyone besides you is whether this has any bearing on how you feel about the person you love, if this is gonna keep you from telling them- or if you tell them how you feel if you wanna tell them about what's happened or if you wanna keep it all to yourself and quietly pine or box up that emotion to never ever be dealt with ever. Some of these things are healthier than others. All of 'em are valid.