My girlfriend of 3.5 years cheated on me. I’ve never felf this way in my entire life. Please help.

We’re both 21, in college. She’s studying in our home country, whilst I left to study abroad. You see where this is going.

Yesterday I found a strange message on her phone. When confronted about it, she seemed really dismissive and annoyed and she kept saying she doesn’t remember, until she suddenly said she only kissed the guy once. Obviously that hurt, but that was not all. After 3.5 years of relantionship you kind of start to really know the other person. I felt she wasn’t telling me the whole story. Lo and behold, after 3 hours of constantly asking her if there’s something else she wants to tell me, she breaks down in tears and tells me she also fucked him once; she kept repeatimg how regretful she’s been this whole time (oh, btw, it’s been 6 months since the cheating happened :) ) and how she didn’t like it; how she only did it because a friend of her told her that she should take advantage of her college time and ‘rack up some experience’.

I cannot get the images out of my head. I cannot understand why the fuck she did this. I cannot understand how she broke my trust so easily. I cannot understand why. I just cannot process this. I’m empty inside, whilst feeling the saddest and loneliest I have ever felt in my life.

I think I need therapy, I feel like I cannot get past this without it. The images man, the images in my head ... make it stop please...

Sorry if this comes of as not so manly, I know you guys are a little bit older and have been through a little bit more in life. I just trusted this girl with my whole fucking heart. Please show me the way forward, I’m just not capable of seeing it. Please help.