phone sex with ex

You guys I need advice. My ex and I broke up about 3 years ago and we've been really good friends ever since. Lately we've been talking a lot at night, nothing serious, just as friends who can't sleep and decide to chat all night. Anyway I have a boyfriend, he's in a different state at the moment, but I love him and I'd never cheat on him. Last night my ex and I were talking as usual, and somehow it just got really weird. He said he felt like there was sexual tension between us, I didn't take it seriously tho. Somehow we ended up having phone sex, and getting off of each other. We decided to pretend it never happened and never talk about it. I feel really guilty, don't know if I should tell my bf or just let the whole thing go. I feel like a shitty human being right now , and I'm just confused on what to do.