To "lose touch with" someone means to stop communicating with them. It's kind of the opposite of "keeping in touch with" someone.
When you "lose touch with" a person, you stop calling or e-mailing them, and you usually don't know what they've been doing recently.
To explain how long it's been since you contacted a person, use "for":
We lost touch with each other for a few years, but he called me last spring out of the blue and invited me out to lunch.