Why would someone hold eye contact for a very long time?

I have a coworker and were friends. We talk a lot during down time. But I noticed that once the conversation ends he's still holding eye contact it's to the point where I look away for a second or two and when I look back he's still holding it. I have to look away for several seconds to break the eye contact completely because it feels a bit awkward for me at least. Why would someone hold eye contact for that long?