It may be that the only reason you really cherished that goal is because it's negativity attracts you somehow - let's say that your life is generally good and you don't feel much emotion, except the thrilling of having that challenging goal.

What you're demonstrating here is that, given a choice, we are always attracted to some kind of energy flow through us (even if a bad-feeling one) rather than no energy flow at all. See Where does apathy fit into the Emotional Guidance Scale and how does a person get out of that feeling?

how to fill the void created by giving up a goal that you have been dragging for years?

The good news here is that you can never truly give up on a goal or, rather, the strong desire that led to you setting the goal in the first place. The reason for that is that in the launching of that desire, a non-physical part of You expanded to make that desire a permanent part of that Bigger, Broader, Non-Physical You. (See What should we imagine, visualize or believe?)

Now you can't go back to being who you were before you had the desire because you're now a different person...the Physical side may appear to be the same as before but the Non-Physical side is most definitely something different.

So if you can't go back to the previous You, what happens when you "give up" on your goal?

The answer is that all you are really giving up is your resistance to the goal. In other words, giving up on a goal that is not good-feeling to you is an excellent first step towards receiving it :) (See the title of the most highly-voted question on Inward Quest)

Giving Up is actually my preferred method of goal-setting these days :) In fact, it's my preferred method of task-setting also...decide what I want and then give up on it - or rather, just let the Universe sort out the details while I do stuff that feels like fun instead of stuff that feels like hard work. (See Abraham's Placemat Process)

It's a highly effective method for getting things done without getting things done :)

As for your main question...

how to fill the void created by giving up a goal that you have been dragging for years?

Going back to the apathy answer link, the "void" you refer to is just the feeling caused by an absence of fast energy flowing through you (i.e. the "void" of being out of touch with your Bigger, Broader self)...so the solution is just make some firm decisions (about anything) and watch how that void starts to disappear as the life force starts to flow through you again.

In a nutshell, the solution for filling the void of having no goals is to set some goals :)

EDIT - Dec 5, 2016

Stumbled across this Abraham recording talking about "giving up" which seems to fit in here...

https://www.youtube.com/watch?v=vu0XQzGPD9s

I know that there are many answers to that question, as many as the number of people who decides to give it a try. I am eager to learn about all the ideas and techniques people can come up with, because I could really use them right now

The people I know (including myself) that at one point decided to give up, did so because of a simple underlying reason. At least this is what I observe again and again. It's because they get fed up with living up to other people's expectations. It could be the expectation of their parents, co-workers, partners, friends or neighbors they are trying to live up to and that bothers them.

Most of us don't really know what we want until we really know. And what I mean is that often our desires are not truly what we want but they exist to prove someone else wrong. Once we prove them wrong or we get fed up with proving them wrong, we now begin to realize that it was never our true desire anyway. It was just a way to make them accept that we are worthy instead of accepting it ourselves first.

So what I did in these phases of being fed up and deciding to give up was to do what I really felt like wanting to do. When you give up trying to prove other people wrong and you really mean it, you now begin to feel what really feels like fun to you. So my advice would be to do what feels like fun even if it never gets you anywhere or the potential result of that fun is likely to never prove anything to anyone. It could be a hobby or just going for a walk for just for yourself just because you are worth it and you feel like doing it. You don't need any other justification than that.

Decide that having fun is more important to you than losing reputation or being judged. And just let life guide you from there.

"Until you have lost your reputation, you never realize what a burden it was or what freedom really is." - Margaret Mitchell