I Lace my BOYFRIENDS underwear with strands of hair to see if he cheats

I'm a 19 year old girl, my boyfriend is 20. We've been together for 2 years now and through out our relationship he has cheated on me a lot. He told me he was going to stop and that he was going to be forever faithful to me so he offered to let me see his phone and check up on him whenever.<br><br>I did but he got bored of that fast so I had to come up with other ways. I started putting strands of hair in places around his room, inside his underwear, under his phone case, on his shoes etc. I check it when I can, and when I do I can tell if he's been with someone because that particular strand of hair would be gone.<br><br>Today I checked and the hair strand from his basketball shorts was gone. I confronted him and he told me he had a party to attend at one of his friends house and he cheated on me.<br><br>I don't know how to move forward now. I feel gross, I feel like a fool for putting such trust in him after he cheated numerous times already. I don't know why I've let myself stay with him for this long. Am I stupid?