Open Relationship Blues

I'm in an open relationship with Alex, and it's been rough lately. I've found myself drawn to someone new at school, but every time I think about pursuing them, the guilt sets in. Last night, after a couple of drinks, I ended up kissing this person. It was amazing, but when we parted ways, I felt like such a liar. Alex has been so supportive and loving, yet here I am, sneaking around with someone else. Today, as much as it hurts to face them, I know I have to tell Alex what happened. I feel stuck between my heart and the rules of our open relationship.