. . . I find that once a relationship goes stale there is no getting it back.  This worries me because, what if it never stops?  Is there a way to recapture any of the original spark? . . ."

From your note, I presume you are talking about a romantic relationship.  Here is one technique to rekindle the memory of that spark, which is a first step to getting it back:

Enhancing a Relationship by Recalling the Original Connection

Imagine you are taking a walk;

Just you and your dog;

You and your dog and a friendly sun and a gentle breeze;

You, your dog, the warmth of the sun and breeze, and an intriguing vision.

Your eyes a drawn to a another walker, a stranger for the moment,

 complete with dog, an appealing face, and a style that makes you want to see more.

Closer now, and witness an expression that births fantasies of a kindred soul.

Yes, it’s true, you can now see in this person’s eyes, a look that is probably just like yours:

We want to know each other.  We can definitely play.

Speaking now, and it’s only getting better.

Thoughts arise — there’s nowhere you could be right now that you wouldn’t like better

with this person next to you. 

At this exact moment, with the scene missing nothing but a music score;

at this perfect meeting, now imagine:

the dogs get in a fight.

Snarls and growls abound, with each pet projecting the kind of canine rage,

that tells you they think you’re behind them 100 percent.

Grabbing them off, holding them off, anticipating the lunges,

while checking your dog’s coat for signs of blood.

“Make sure you keep your dog off mine,” you order the stranger,

as you eye the other dog warily.

“Well, you too.  I think your started it anyway,” is the retort.

Unpleasantly engaged by the dogs for a couple of minutes,

you don’t notice that you are starting to forget the first five minutes you shared,

but you each begin to have the last connection you will ever share, a common thought:

“If I just go away, I won’t have to keep this up, the struggle will be over,”

and so, with a helpless glance, you leave.

When this happens in a marriage, it’s called a divorce.

This  problem is normal, unfortunately.  It is the most difficult to be ourselves with the people who matter the most to us, because of the stress of knowing how much they could hurt us.  

To remember why you began to hang out with your friend to begin with, do this:

— Write down four recent enjoyable events, not involving your friend. (big or little)

— Next, add four qualities you enjoy about yourself. (adjectives, characteristics you have ever evidenced)

— Now, four qualities you enjoy about your friend.  Not the only four or best four, any four.

— Finally, four times you enjoyed with this person from whenever, even the first five minutes you met. 

There is no way to do this wrong, except to qualify it.  It already goes without saying that none of these positive events or qualities are all the time, so you don’t have to say it.  As you do this, you’ll remember what the couple with the dogs forgot. 

Ask your friend to do this, too.  If you get agreement, set a time to read each one to the other.   Prepare to be embarrassed, maybe to cry.  But, when you are listening, don’t say a word.  Just experience the gift.  Say hello to the sun.