Why do men lie so much?

Not to all men do it. But I have yet to meet one that is completely honest. I keep finding out my bf lied to me about stuff, mostly involving his child's mother but I also caught him texting another girl who he claimed was a boy. And it's not even always a bold faced lie, he just gives "alternative facts". It's driving me nuts, you'd think getting caught repeatedly would make you stop making a fool of yourself lol