Existence has no opposite.
metaphysics - Can a complete opposite even exist? - Philosophy Stack Exchange
metaphysics - Is contrast necessary to existence? - Philosophy Stack Exchange
Does the existence of one thing necessarily imply the existence of its opposite?
There is no alternative to existing. You can't not exist.
All of it is a matter of point of view.
When you see fast and slow for example, I only see different degrees of speed.
Human is really good at making opposites probably because it is easier for us. It is more like the human brain built all the contrasts to make it easier for us. Fast/Slow, Good/Bad, High/Low are bounds of our vision and there is many thing between you can't describe.
Also, nothing tells us that the notions you talk about exists. If these are abstractions we built, there is probably no fast and no slow, no good and no bad, no love and no hate. There are simply notions you can apply to situations.
For example, when you are on a highway at the right speed, you can't tell you're going fast or slow. It is just something between you can't describe. And maybe you can't describe them because you don't have a definition of them. And maybe you don't have definition (nobody have one) because these things don't exist.
Existence:
(Meaning)
1.The fact or state of living or having objective reality.
2.Existence is the ability of an entity to interact with physical or mental reality.
For existence of an entity, contrast is necessary.
You gave a few words and their opposites to convince the necessity of contrast. But before dealing this word--existence, we should think whether existence has an imaginable opposite. We may be using the word 'nonexistence' as its opposite. But what is it? Is it an abstract noun actually?
So, for existence there is no need of a contrast. But to know the existence of an entity, contrast is necessary.
For the existence of the Ultimate Truth, no contrast is necessary. In other words, if there is Ultimate Truth it must be the absolute existence.