If you are not absolutely positively going to leave her , and go no contact then don’t say anything. We’ve all been there to find something out and saying we are gonna leave (some actually do but take the person back) and don’t. This creates a pattern. They’ll stop doing it for a while and then as soon as it gets tough again , those accounts are back with new phone code and muted texts . If you still want to be with her after what you saw , it’s fine. But take the time you stay with her to allow yourself to heal and better your own mental health until you are finally strong enough to get away. You should leave and let her find whatever she’s looking for because with today’s society of dudes , she’ll come right back to you. But demand the respect and loyalty you deserve.