It's a betrayal if you believe it's a betrayal, and it's wrong if you think it's wrong. Just like snooping is wrong if the snoopee thinks it's wrong. This isn't just moral relativism - it's about what matters to *you*. It doesn't matter if the rest of the world approves, accepts or can forgive the actions in question. The critical thing for *your* mental health and ability to carry on your side of a future (healthy?) relationship is whether *you* approve, accept and/or forgive.

If you consider it an unforgiveable betrayal - if it continues to bug the shit out of you for weeks and months after it's been discovered and discussed - then it really doesn't make any difference whether we approve or if *he* thinks it's acceptable. If you two can't come to an agreement on this, and you put in as much ego-free consideration as you're capable of, then it's likely as much of a deal-breaker as if he thinks that your play and attempts to emulate aren't enough.