>think it happened was that his friend came out during this time that they were apart and realized he had feelings towards your boyfriend back in their military days and he unfortunately did this.

This is my instinct too.

Those who serve together in the military develop a very close bond, and unfortunately that likely made it harder for the bf to resist the temptation to cheat.

He still screwed up, BAD, but cheating with someone you were in literal life-and-death situations with is at least a little understandable.

>Since you two have this intimacy of using each others phones, just be honest with him: tell him exactly what you told here about you trying to take a picture of your cat, that the message popped up and you couldn't help feeling uneasy... it is an extraordinary thing to happen to anyone and I think he'll understand why you read their conversation.

Honesty is indeed always the best policy.

A lot of people here saying "fuck it, he's a cheater" need to realize cheaters are still human- and there's no reason to make things worse with them than necessary.

It reminds me far too much of how people treat drug addiction, the homeless, etc. I.E. dehumanizing others. Sadly, most of us could have been in their shoes were our upbringing and circumstances different.

Also, this kind of dehumanization becomes so toxic that people can ruin someone's reputation merely by spreading falsely rumors of past drug use, sexual deviance, etc.

I know my father spread such completely false rumors about my mother after her divorcing him, for instance (in reality, he cheated on her).

So, don't get in the habit of dehumanizing others.