Wow 4 years at that age.. you must have been doing a lot right!
Seriously, there would be a tiny tiny percentage of people who get a girlfriend at 16 and end up spending their life with them. If I were you, I would have been waiting for this day to come. Not much you can do but get out there and enjoy yourself
Don't get into another full on relationship for a while, have some fun
That's a pretty good run imo