Well, obviously I'm not a man, and probably can't speak for one with legitmacy...
However, experience has taught me that of the two species....male and female...I think females keep up their end of the lying habit. I've known many who couldn't tell a boyfriend/spouse the truth if it sounded better.
A man probably lies for the same reason anyone does: there's an expected pay off somewhere in their mind for the lie. Either they think it's better to tell someone they're involved with what they want to hear, or they think the truth will hurt the one they are with, or it will hurt themselves.
Sometimes it's just a lazy habit. There was a couple we had been friends with "forever" and the man told more lies than he could count. If he was opening his mouth, he was lying somewhere in the sentence he spoke. For him, I think it was a compulsion, a disorder; he always spoke in words what he wanted to have happened. This lifetime habit caused him and his wife, and children much misery. He had other redeeming qualities, and we could walk away when we got our gut full, but his family of course, could not.
Encourage truth by being strong enough to handle what we may not want to hear. Praise truth and model it in our own lives, and I think we'll see it more in those who mean so much to us.
If not, walk away. Habitual bad lies are harmful.