My gf cucked me our entire relationship and had no idea [cuckold perspective]

So for most of the relationship, she had no idea I knew she was cheating. she went out with her friends that were in a sorority. Her friends lived sorority house like 5 minutes from me. So they went out and she stopped answering me. I knew she was still out cuz I had her location. I ended falling asleep and woke up the next morning and she still wasn’t home. I saw her location was at the sorority house. I’ve been there a bunch and knew they left the back door unlocked. So I went over there to see where she was. When I walked in, a big black dude walked out of the spare room and into the bathroom Completely naked. His cock was soft and still massive. He made eye contact with me and smirked. So I peaked into the spare room and saw her sleeping in the bed, completely naked with red hand prints all over her ass