I'm not sure you're differentiating between lust and natural, normal desire. It seems to me you're not, but I could be wrong. To have or sustain such a desire for a married woman is lust - to have it for an unmarried woman is not.
These verses from Deuteronomy 21 - rules God gave for an Israelite man who found a beautiful (captive) woman he decided he wanted to marry - would you describe these as lust, or natural desire?
10 When thou goest forth to war against thine enemies, and the Lord thy God hath delivered them into thine hands, and thou hast taken them captive,
11 And seest among the captives a beautiful woman, and hast a desire unto her, that thou wouldest have her to thy wife;
12 Then thou shalt bring her home to thine house, and she shall shave her head, and pare her nails;
13 And she shall put the raiment of her captivity from off her, and shall remain in thine house, and bewail her father and her mother a full month: and after that thou shalt go in unto her, and be her husband, and she shall be thy wife.