Personally I would leave. I know myself well enough that I know I would be unable to fully trust this person again to the extent that is needed in marriage. Some people can, but I can’t (choose not to). I hope that you are better in that respect if you hope to restore your marriage. You seem to not know why the betrayal occurred, I would say that you should at minimum see a therapist to determine why, before you decide what to do going forward. Good luck!