Straight guy? ..Wait he like me but at what price?

Guy at job that I thought was straight likes me. He constantly stares at me and is sweet to me when we're alone. When we're around his co-workers he pretty much ignores me. He always checks for me when he walks by. We always stare at each other and every time the world fades. My good friend found out that we both graduated from the same school in the same year and interned at the same company. He's gets super reserved/"Straight" when I come around him when he’s with his co-workers. He started to ignore me but still stares occasionally after he saw me with a male co-worker walking by. Ever since then he's changed. The one I was walking with has a girlfriend and were just walking together talking. He was just staring at the both of us like.... I don't know. I'm just heartbroken. Should I just ignore him to feel better? I see him three days a week!!!