You are boring to him. Or perhaps you have done something that has taught him going to you = end of fun times. Like, you maybe call him to you to put him inside or make him stop doing something naughty etc.
The BEST tactic is to make your dog realize that going to you is the BESTEST MOST AWESOME thing in the world. And you accomplish that by carrying super tasty treats on you.
Also I suggest changing the "come here" command because by now you have probably "tainted" it for him.
Make up a new word for "come here" and call him... and praise HEAVILY with very yummy treats when he comes.
You have to be very consistent and every time you say the command, he has to get the yummy treat. After some weeks you can start giving him the treat every second time or so... but you must get it really solid first.
Good luck!