I can't say there's any quick fix.
This is all about something that's taking place in your mind. That's where the real battleground is.
It's part habit, it's part brain chemical reaction. We're humans, this is how we're made to operate.
I can tell you that adopting zen philosophies can help a lot. It's quite like therapy.
Basically, you've become emotionally attached to someone who's no longer there. So you feel that absence. The PEA "feel good" brain chemicals that she stimulated aren't being triggered anymore, and like an addict, you're seeking a fix.
The habit of your routine with her has you stuck.
As human beings, we then aggravate that circumstance by dwelling on it. You see, a dog gets its leg chopped off in an accident and after the initial pain, forgets all about the accident and makes do with three legs and moves on, happily wagging its tail.
We, on the other hand, relive the pain of the breakup over and over again, by dwelling on what could've been, what happened, what was, what isn't, what now will never be, and in the process creating misery for ourselves and lamenting over our loss.
If you're in misery for a year, that's equivalent to reliving your pain 365 times.
So pain is a given but misery is optional.
So what to do?
GAL: "Get A Life". You touched upon that. Stay busy. Preoccupy yourself with endeavors, new and old. New hobbies, old hobbies, new interests, old interests. Sports is real good because you can't dive into a pool or watch a baseball coming at you at 90 miles an hour and be thinking about your ex at the same time.
You're basically trying to get out of old habits/routines and put on new ones.
But there's more benefits then just that. New experiences make you grow as a person. Personal growth makes you more interesting to others. You meet new people. New doors open to yet more new experiences.
I went from kicking out my ex-wife to acting off-off broadway and in indie films. That probably would not have happened otherwise.
GAL also "shrinks" the ex's importance in your life the more you make other things bigger. Yeah, you'll have moments, but that's normal. Just don't keep backsliding but push yourself forward. It's like waves upon the shore, ebbing and flowing, until you're finally back on land again.
Stay clear from alcohol, that's a depressant. there's a reason guys "cry" into their beers.
And when you get triggered, like something reminds you of her, replace it with another thought immediately. Know that such thoughts will only bring miserable feelings if you let them stay on your mind, because feelings follow thoughts. This is why we can be happy but then hear some sad news, and then feel sad.
Thoughts are going to pop into your head, but you don't have to dwell on them. Remember: you can't stop a bird from landing on your head, but you can stop them from building a nest there.
Dating around may not be good for you until you're okay. Until then, you may be seeking a replacement, which many guys do but is the wrong reason to be with someone. Or no one may seem to compare with the ex, which is normal but only because you've glorified her in your mind. So, just go out to have fun for now.
Nothing lasts forever. This too shall pass.