How do most divorced parents decide custody?

[KamiGirl]

My divorce has been final for almost a year. We've decided to share custody with our boys (5&8) alternating between each household on a weekly basis. (One week, Friday-Friday, with me and the next with their father.) Their father has recently stated that he thinks that it would be best (and more stable) for the boys so be in a single household on a permanent basis with visitation allowed for the other parent. I, on the other hand, think that we should each have equal opportunity to spend time with and raise our boys as we are both equally important in their lives. (FYI, He didn't say who should have custody and who should have visitation.)

I don't know very many people in my situation, so I come here to pose my questions . . . Is this a normal arrangement of custody? 50/50, alternating each week between parents. Or, do most people have one parent with sole custody and the other with visitation? What's better for the children? Any experience-based advice is appreciated!

Thanks!
We don't have open communication. He sprung this on me last night, via e-mail! I think that this decision stems from his girlfriend (she's young, 22, and I understand not wanting to deal with someone else's children), however, I believe that children need both of their parents in their lives (if possible, and, in this case, it is.) I couldn't bear seeing my boys every other weekend and don't understand how he could WANT that. I guess I'm just really biased about wanting us both to be involved in raising them, but, at the same time, don't want my desire to co-parent clouding my judgement.