What acts constitute adultery as put in Leviticus?

I have found only one page that but slightly touches this subject:

http://mobile.jewishvaluesonline.org/question.php?id=1162

What would make a woman forbidden to her husband and liable to the death penalty? Petting with another man? Sex “by way of the members” and oral sex?

There are discussions on the subject of sex stating that only penetrative sex would count as the ultimate misdeed, but that would not sufficiently explain why Rebecca is described as a virgin and a woman who had known no man, as well as the punishability of lesbian sexual acts, deemed “mere lewdness” by some but put in the same category as male homosexual practices by Paul in Romans.

Finally, what kind of punishment would men receive for breaking their marital commitment?

This is out of genuine curiosity and not intended to be some wanton post.

Also sorry for the wordiness.