I'll offer some advice on this as I recently have had some similar realities come to slap me in the face so to speak. I have been married for 12 years and with the same girl for about 17. We have two beautiful kids, new cars, a nice house, good jobs etc.. We are both somewhat possessive of each other and have our own insecurities about some things, probably from earlier relationships. We are built differently when it comes to emotions. I am somewhat standoffish and cold, and she isn't. She is like most women only to a higher degree. What I mean is, she NEEDS to be told Ilove you and complimented alot. I swear I don't know how we made it as long as we have cause that is not me. I don't do that very much. About 10 months ago we had a decent argument. We hung out all day with friends we have known for bout 15 years when she got mad at me about something. Anyway she had been acting a little guilty/shady for a few days prior and i had been noticing it. Anyway long story short I checked her phone for some pics of the day we all hung out and found a picture that I was not at all happy with that wasn't sent to me. It wasn't horrible, but with my demeanor it was unacceptable. She lied about who and where it was sent and after 8 months of constant arguing, she finally admitted what I already new. Although as far as I can know, there has been no actual cheating physically, but that was cheating to me. It was a friend of mine , who no longer is. I can tell you this, that is not something you are soon to forgive or forget. Reason I tell you all that is, somtimes women will do stuff for shock value to let you know they are not happy. They need constatnt reassurance that you still want them and you love them. I failed at that, but know I am not responsible ultimately for her actions. She is a grown women. She makes her choices and has to deal with the consequences. However, if you love her, or if you think there is anything in your marriage worth trying to save. You have to talk to her and explain your side of it. Then you have to let her explain her side of it. And lay it all out there. In the end, what did you lose by talking about it? If it is unrepairable then so be it. I'm not judging either of you as I don't know you, but I'm telling you my experience on a similar issue, so you see both sides. No excuse for those actions, but let her explain where and why she did what she did. If you catch her in a lie then the answer is in front of you and still you haven't lost anything more than you would have originaly. Just my two cents. Good luck though man, it sucks.
By the way...there is plenty of electronic gadget floating around that can help you determine for sure if anything is going on with another man (or woman) as the case may be. They are relatively inexpensive too.
just sayin. God I loved my job as u/c detective.