If you look at the passage in Matt 5:28 in the greek you find that the lust verb applies to the woman.

"If you look at a woman so that she lusts"

In my mind this implies flirting.

But even if we go with the traditional english translation.... what does "so as to have passion for her" mean?

I don't think it means to desire her sexually. I think it means to make plans to pursue her sexually. There's a huge and significant difference in my mind between admiring the sexual beauty of someone and coveting to posses that beauty for yourself.

I think if Jesus meant that just to see someone and think they were erotically attractive were sinful then we really would have to pluck our eyes out to stay pure.... but then... what if they have sexy voices!

Blessings
Cat.