A very fortunate few do find a beautiful love with another, but it will run its course and finally end, even if it lasts a lifetime.
This is a sobering thought - and might not brighten your day - but contemplating the true flow and the temporary nature of everything in life is a huge step towards experiencing an inner letting-go of mind-made ideas that control our thinking, our feelings and our behaviour.
Nothing lasts forever. Whether the soulmate idea is real or not, every relationship is finite. It is scary to truly accept that nothing external, whether a person, possession, or even our physical body, will last forever - but it is fact, it is truth. Everything can, and ultimately will, leave us.
Somehow, although there is no way to explain how, when we truly deeply accept that all things will pass, we relax our grip and begin to appreciate and enjoy it all the more. As this happens, simultaneously our mental/emotional attachment and clinging to what we might lose, or what we feel we could not live without, begins to lessen. And when we stop trying to hold onto anything, what is meant to be with us naturally stays and things that do not serve us start to fall away.
Love, when in relation to something external, is the most powerful emotion, but if we genuinely look at where it comes from, we discover that it is an expression of something deeper that is just 'there, on the inside'. Looking inside, love cannot be found as an object, although it is often felt to be vaguely in our heart rather than in our mind. By focusing attention on the source of love we can get past the obstruction that is an idea that we must have something - something - a person, object, idea or belief - to love. When you discover that love is there even in the absence of an external object, spontaneously our 'longing to love' is set free to flow out unconditionally.