No idea what to do

So I've got a problem and I don't know what to do.
My GF of 17 years is, at the very least, talking to and spending time with another guy behind my back and I'm very worried it could be more.
I've never been worried about something like this before in the whole 17 years of our relationship. She's always been very passionately in love with me and usually can't stand being apart for me from too long. She's always been a very social person, but not flirtatious and, above all, she's never been in any way secretive about the people she associates with.
Our relationship went through some problems over the past few years when she developed a heavy drinking problem. Things were very bad for a while, and I had to threaten to end things, but she got sober earlier this year and things really started to improve for a while. It's worth noting that, even while she was drinking, I never suspected infedility for a few reasons, but mostly because she was never dishonest about who she was with and where she was.
That all changed a couple of days ago. She relapsed in her drinking over the holidays, and I went through her text messages to try to get some more info about the extent of the problem. Instead, I found a long text message thread with some guy I've never met or heard of. Apparently they met at a bar near us a few months ago (it also appears her relapse has been happening longer than I thought). The texts start out fairly normal - it was nice to meet you kind of stuff before progressing "omg it was so good talking to you last night" and "I can't wait to see you again" type of stuff. Then he sends one asking her if they can hang out "somewhere besides the bar" to which she replies "sounds like a plan".
Now, let me say up front that there's no kind of "proof" they did anything physical, and it's even possible they haven't yet (although I'm very worried). But there are texts where they're planning to meet up and do things and even texts about her going to his house to have dinner and even sleep there (just saying things like "I'm sorry I woke you up with my snoring", but still). And the kicker - there's a text about her going over to his house to hang out the day after Christmas, when I thought she drove to the suburbs to visit her mom and slept there.
There's also frequent half hour long phone calls between them and messages from her like "can't wait to talk to you", "you looked so handsome last night" "you should come hang out with me I look great right now" and even a late night drunk text asking if she can "come see you right now" (which he didn't answer, and she apologized to him the next day for drunk dialing him).
I have no idea what to do. On one hand I don't actually know for sure if this is a physical affair yet or just an emotional one at this point. I don't have any proof of anything that she couldn't easily deny or minimize and I came about it in a somewhat unethical way (by going through her text messages, which I acknowledge I shouldn't have been doing in the first place). I also feel like confronting her with it will just teach her to make sure she deletes anything she doesn't want me to see in the future. On the other hand - I wasn't born yesterday. I know that there is something serious going on, but I don't know just how bad. I know I have to do something, I just have no idea what. I've never been in a situation anything like this before. This has all struck me out of nowhere and I feel like I'm still in somewhat of a state of shock. Any advice anyone can give me would be greatly appreciated.

7 comments posted: Friday, January 2nd, 2026