And then there is the 'self' -- that entity that we are told has meaning only in relation to another (socially sanctioned) 'special' one. But the fact is, it continues to exist... with or without love, with or without partner. All flesh and marrow, skin and bone, spine and skull, and a beating heart left of the torso. It is endowed with the same five senses as others (who are coupled) that responds to the same four elements of Nature, the same four seasons, the social environment and fellow sentient beings. The perceived 'lack' in its existence may be a result of both circumstance and choice, but that doesn't take away the validity of its presence in the world. And its relation to itself.
Romantic love is at worst an illusion, at best an episode in most people's lives. For many others, it's a luxury they can't afford, though they may long for it - like diamonds on billboards.
And some are so broken inside from past betrayals and take so long to heal that the possibility of 'new love' becomes redundant for them.
Taken together, these people probably account for the majority of human beings on earth. One realizes then why the disproportionate presence of love in poetry and song and story: they articulate a desire, not a reality.
Ultimately, the self - and the body it's clothed in - is one's longest, uninterrupted companion in life.