There is a wide range of what people consider cheating. Some people consider looking at porn to be cheating, while others say sexual encounters don’t count out of state. There’s also a difference in whether people consider “cheating” to be a hard line that’s been crossed, or whether there are “degrees” of cheating. There’s also a distinction between physical and emotional infidelity. Some people may say that emotional infidelity isn’t “cheating,” while others might say it’s worse than acting out physically. Ultimately, it’s a distinction that each individual draws based on their principles, their feelings, and agreed-upon boundaries and understandings within a monogamous relationship.
My personal take in your case is that “cheater” is a strong word that lays down a hard line, probably too much so, but that you were somewhere in the gray area between fidelity and betrayal. In marriage seminars I’ve attended, and in my personal experience, the cliche “if you play with fire you’ll get burnt” applies. Maybe you didn’t reciprocate the flirting and memes, but allowing that communication to continue wasn’t productive for your relationship. I also wonder why, after all those years, did you reach out to this person? I can only speak for myself, but I know in the past when I reached out “just to catch up” with someone, I half hoped they would flirt.
Gary Chapman once said that after awhile of being with the same partner, it’ll feel settled. You will encounter people who make you feel tingles again. It feels good–that’s how we get into relationships to begin with. When that happens, if you value your relationship, don’t stick around for it. If you think you can handle the tingles, eventually they’ll build up until you lose yourself in them.
I can imagine that having someone flirt with you felt good. It’s only natural. We want to feel desirable and be desired. If it was unwelcome, you wouldn’t have tolerated it. Your boyfriend was probably hurt to see that flirtation, even if it was one-sided. He probably sees this other guy as a threat. Even if you didn’t engage in the flirting, the guy was clearly coming on to you, and in your boyfriend’s eyes you were allowing it to happen by not saying “I can’t have you talking to me like that” or blocking him. Maybe you didn’t cross any boundaries yourself, but that guy crossed boundaries that were thought to be understood.
I do think, however, that labeling you as a cheater is precluding the chance for you two to have a productive conversation about what happened and why. Instead of coming through it together, your boyfriend has declared you in the wrong, which implies that the only way forward is for you to apologize. These things don’t happen in a vacuum. They happen when something is missing in a relationship, whether it’s the thrill, affection, or acknowledgment. An old boss once told me “In a relationship, you can be right or you can be happy.” As I have grown with my wife, I have found that that idea doesn’t mean deferring to your partner, it means not trying to one-up them. Let’s say he’s lost on a drive and you were right about the directions. You can rub his nose in it, but that doesn’t serve your relationship, it just makes him resent you. In this case, he’s calling you a cheater, but does he win a special prize for it? It would be better for both him and you if you could talk about it and come through it together. That’s on him though.
It sucks that you’re going through this. Calling someone a cheater, using those words, isn’t something a person can just take back, even if you’re completely blameless. It’s a crack in your mutual trust that needs to heal. I hope you and he can reach an understanding and work through it, I hope it doesn’t take too long, and I hope it can be a growth opportunity for both of you. 