Around a decade ago personal relationships were described by expressions like 'we hit it off' or 'we gel well' with each other. In current parlance it has changed to 'we've got chemistry' or 'we have matching chemistry'. Behavioural parameters like love, hate, rage, anger or pleasure are the result of an interaction between "neurotransmitters" and "hormones" influenced by the environment which provides the 'set' and 'setting'. Emotions come straight from the heart, and are powerful enough to connect our souls and the body. Many interacting chemicals in the body are involved, and the final outcome is portrayed as the behaviour in that particular 'set' and 'setting'. Lets consider the salient features of some of them:

Phenylethylamine (PEA) is a brain chemical that acts like the central nervous system (CNS) stimulant, and the body reacts to it as if one was on "cloud nine". Another effect of PEA is to release  dopamine, which is a neurotransmitter that sends messages from one nerve cell to the other in the brain. It boost our energy level and motivation.

Testosterone is the 'hormone of desire'. It is present both in men and women. It is released to prepare the body for love and intimacy. Perhaps that would explain as to why one is sexually more active in the early days of marriage. In excess it also results in aggression and rage. 

Noradrenaline and Adrenaline are sympathomimetic agents which increase the blood pressure and heart rate, and prepare the person for 'fight and flight'.

Endorphins function as a built-in reward system in the body. These are neurotransmitters that are released in the brain to reward us for good behaviour, and induce a feeling of happiness and pleasure. Endorphins motivate and energise us to feel happy and alive, because of which we can cope with 'stress' easily.

Serotonin is a neurotransmitter which more so in women is responsible  for inducing a feeling of comfort, relaxation, contentment and optimism, provided the husbands provide them the opportunity. Serotonin as such is mainly involved in mood regulation, and basic activities like eating, sleep, arousal, control of pain and formation of memory. Serotonin also influences judgement-making about people in close relationships. 

Oxytocin is the 'cuddle' hormone, and its release is increased by serotonin. It has also been known as"the hormone of love", and is the key to lasting relationships. Oxytocin also releases testosterone flow and endorphins. 

Thus, the 'science of relationships' involves many intricate balances between 'neurotramsmitters' and 'hormones' in the human body. Simple, truthful, and honest lifestyle allows these interactions and balances to continue uneventfully though our life, providing us the pleasure of living.