There are a lot of theories on human needs, like to reproduce and to feed where the common denominator is the survival of the species.
I have not seen it but I believe someone must have identified the need to love and be loved.
And we all know from personal experience, I bet, how lonely and depressing it is not to be in a loving relationship.
It is not the need for affiliation. That need is from your brain, to socialize, to interrelate. It is not the need for sexual release either. It is to love with your heart; To ache with your heart for someone.
If you cannot get it from a human being, get a pet.
Research shows that even hard core prisoners get humanized when given a dog to raise. The love that dog gives to them changes their behavior better and faster than any talk therapy.
Maybe they became criminals because they were deprived of this most basic need of all: to love and be loved.
We are trying to solve our problems with our brain, analyzing cost benefit ratios. The real, sustainable solution is processed by the heart, where we feel without having a clue of the ratios.
What interferes with this need to love or be loved is the brain, with all the other needs it has to process. One of them is fear, which is related to the need to survive. Another is to achieve; we are so busy with a career we have no time to feel and be loved by another person.
Calm the brain. Think less and let your heart manifest the love it naturally has.
Ichak Kalderon Adizes