Okay...think about this...
You were in a relationship. You were happy. It was positive for you not only sexually, but emotionally. That all sounds good so far. The only thing that's "wrong" with it is that society doesn't approve of it and sees it as abnormal.
Don't think it's tainted you. Older men aren't somehow corrupted, at least, no more than younger men. People can be loving or compassionate or intelligent at any age; conversely, they can also be selfish or controlling or ignorant at any age. How old someone is is inconsequential with regards to how good a partner they are.
I would try to not feel guilty for being in a relationship with someone who made you happy. Isn't that what we're all looking for?
I've been in one brief relationship with an older man (the age gap was very similar actually). People sometimes gave us funny looks, but I just shrugged them off. I found that, with friends (and other partners), it's best to just not make it a thing. Don't, like, shove it in their faces, but if it comes up just talk about it the way you would any relationship. Humour can help defuse awkward situations; funny stories where the age gap led to misunderstandings, good "and my parents almost caught us tales, etc...dot hide it. Hiding information gives it a value and an import that it just doesn't have if everyone knows. People can't tell their friends if you've already told them.
I'm not sure why you might regret it; do you feel guilty about hiding it from your family? Because, again, being in a relationship with someone who makes you happy no matter how old they are is not something to feel guilty about.