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.
Secrets said everything that everyone would here would tell you. Dogs don't do anything for no reason at all. You could imagine that in the wild, if dogs didn't behave in ways that got them food, water and companionship as efficiently as possible, they would be an extinct species. Likewise, dogs don't listen to humans unless they believe that it is important to getting a reward. Much like human kids, they don't magically listen just because someone bigger and older told them to. Food is the most obvious reward, but things like praise and play can be very motivating as well.