lust is an inordinate craving for coitus often to the point of assuming a self-indulgent, and sometimes violent character
a genuine love affair has passion and sexual excitement as well but it is not lustful since it is carried out by two people in love.
admittedly some men treat their wives badly but that is the exception not the rule. most men have genuine affection for their spouse and would never act in an inapproriate way just to get sex with them.
yes they want sex and they may even have to lose their dignity and beg for it occasuionally but they seldom just take it by force and they usually want consent at least and full active participation and enjoyment. it is not a self indulgent act to make love to your wife