Is Sexting Cheating?

My wife was texting an old flame from High school for the past few months. She said she called it off about a month ago and that it was fairly innocent. Saw messages on iPad that were "deleted" but not forever and they go back to the beginning. It wasn't all that innocent after all and they kept discussing getting together irl, but never actually did. The last message to be fair was her telling him she can't do it anymore and him saying he understood but it has me so twisted. Weve been married for a long time and have kids, dogs etc. I'm telling myself I'm willing to forgive her, but something inside me keeps questioning whether that's the right move or not.

Could REALLY use some help on this one from the community