Forgive me if I'm misinterpreting some of the posts (as it's very late right now, and in reality I should be in bed!)...
But I had always assumed "monogamous" meant "one partner" and NOT "one partner for life".
When you're in a monogamous relationship, you're only seeing one person. You're not seeing anyone else. This is assuming you're in a committed relationship (ie: you're not playing the field).
Obviously if you're not committed and you're interested in seeing other people without really seriously connecting with any one person, you're not in a monogamous relationship.
If you marry someone one year, divorce them due to lack of compatibility the next year, then re-marry to someone the following year... you're still practicing monogamous relationships. You're just not in a monogamous relationship for LIFE.
Polygamy on the other hand, is where you're seeing/dating/committed to several people at the same time.
Okay, now I'm starting to feel like a dictionary.
But some of the above posts made it sound like if you had sex with more than one partner in your lifetime, then you obviously weren't in a monogamous relationship.
I had always thought that as long as you were committed to that person and weren't involved with anyone else during that relationship, it's monogamous. You're with one (mono) person.
Maybe I should head to bed before I make even less sense...