When Do You Become Exclusive?

When discussing the definition of dating, monogamy and exclusivity invariably come up. It's not enough to just say that you are dating someone when you socially spend time with them in the attempt to pursue a romantic relationship anymore. For some people, dating implies an exclusive interaction while determining whether or not to get seriousl. So my question is this: How long do you think you should two people be dating before it becomes exclusive or monogamous? To choose an answer, click on the appropriate link:

• I know right away.
• Within the first few weeks.
• When sex enters the picture.
• After a few months, we stop seeing everyone else.
• When we both discuss it and decide together.
• If s/he never catches me with anyone else, it's exclusive.
• I don't believe in exclusive relationships.