21 and older: Is it possible that I will get a fourth chance?

It's possible, but (there's always a "but," isn't there?) you don't say how long you and Chris were together the first time, and how well you got to know each other before trying to start a relationship each time. It's possible your sixteen year old self built this up into a star-crossed love affair for the ages, when you might have realized on your own that it wasn't going to work if you'd met as adults and dated without interruption. Don't close the door if you're not ready, but don't turn away other opportunities if they present themselves, either.