There’s this guy at my office...

There’s this guy at my office. He has always had a very happy smile around me and staring at me. We exchanged a lot about works and also about our personal vulnerabilities. He shared with me hard moments for tough decisions in his life. We trusted each other. Someday, I noticed him stalking me around the office and in the street. He eventually got jealous of the guys who approached me. It’s been two years that we know each other. What does all of that mean?