Help a sister out

Me & my boyfriend been together for 2 years now . He was telling me a story about how all his friends got really drunk and he had to take them home. Well while we were having sex in the back seat of his car I found a girl earring that does not belong to me . I immediately confront him ab the shit. He said that it was his friends girlfriends because she was the only female that was in the car when he took them out . I really love him but Ian tryna be out here looking stupid for him . We’ve been through hell and back together but I refuse to drag myself through hell again . What should I do?