When Poly Isn't Enough Anymore

I've been with my partner Alex for four years now. We're both nonbinary and in an open relationship since the start, but recently something's shifted. It started small, I began spending more time with a new friend, Sam, who's also into polyamory and sex positivity. Sam and I clicked instantly over shared interests and kinks; one day we decided to try something casual, like friends having fun together. We were both drunk that night when things escalated faster than expected, ending in us fucking hard against a wall at his place. It wasn't planned or discussed beforehand, but it felt necessary, right then. The next morning, guilt hit me harder than ever before, I'd crossed a line without talking to Alex first. But the sex was incredible, intense and raw; it was different from anything with Alex. With Sam, there's an edge that brings out my kinks in ways I didn't know possible until now. So here's where I am: I'm still seeing both of them, but something changed after that night. Now, every time I think about either one of them sexually, it's hard to separate Alex from Sam and the wildness between us. And sometimes when I have sex with Alex, images pop into my head of doing it with Sam instead. Is this normal? Should I tell Alex what happened or leave things as they are until the guilt passes? How do you handle these kinds of situations without hurting anyone?