Partner of 11 years had an affair with a colleague.

Hey Reddit, The title really sums up my feelings, and I’m not quite sure what I expect to gain from sharing this, but I need to vent and would appreciate any words of encouragement from those who have been in a similar situation. I’m a 29-year-old guy, and my girlfriend is 28. We’ve been together since high school—our first love and our first everything. I’ve poured my heart into this relationship, and she’s mostly done the same for me. However, things have taken a turn in the past few months. She started expressing doubts, which hit me hard. I genuinely believed we would be together forever; we have a home, pets, and our families get along wonderfully. Lately, she’s been very cold and distant, even more so in the past week. I had a nagging feeling that something was off. I suspected she had been out late, claiming to be at a friend’s house, but my instincts told me otherwise. So, I looked through her phone and discovered that she had lied to me and spent the night at a colleague's place. Right now, I feel like I'm living a nightmare. I’m sad, angry, confused, and mostly just defeated. I want nothing more than to forgive her and pretend this never happened. She is clearly feeling the weight of her actions—she’s a mess, overwhelmed with shame and self-loathing. I know the common advice is to walk away, and I understand that may be what’s best. But 11 years is a long time; it feels impossible to just throw that away. She’s never done anything like this before, and while I know I shouldn’t excuse her behavior, part of me gets how she could be caught up in the excitement of it. So, where do I go from here? I have good friends, and I’m fairly intelligent and not bad-looking, so I know I have the potential to move on. But right now, all I want to do is curl up and disappear. Any thoughts or advice would be greatly appreciated. Thanks.