Is it lust when I get married and I use a condom or some other birth control for a while with my wife? I'm confused because my brother says yes and my friend says no. Also, condoms did not exist in the era Jesus was born in. I also heard that lust is a deadly sin and I don't want to ruin my marriage.
Email didn't exist in Jesus' time either, but you are willing to use it to communicate. Right and wrong are not determined by what existed at a particular era in time. See Contraceptives.
A desire to have sex with your wife is not lust because sex is supposed to take place in marriage (Hebrews 13:4; I Corinthians 7:2-5). It is not sinful to want to have sex with your wife; therefore, it is not lust.