basic trade principles that increases value of exchange in a relationship

probably the easiest way to increase sexual/romantic attraction in a relationship is if: 

the woman will sexually satisfy the man with blowjobs and anal sex 

then the man will romantically satisfy the woman by showing interest in her and showing interest in other women, this creates romance and jealousy

and then passion will increase in relationship 

and then woman will more enjoy sex with man 

a relationship between a man and a woman may have started without sexual/romamtic attraction, or that was lost along the way