My story is rambling around in my head

I have a basic premise for my first novel. I have a beginning and a middle but the end is a little fuzzy. My husband keeps adding in his thoughts and it changes the story a bit or at least it changes my thoughts about the story.
HOW to write the story is what I'm trying to figure out.
Back and forth from chapter to chapter? Like, one chapter it's one scene and another chapter is another scene and back and forth?
Or write it in a linear way? Even though it's not exactly a linear story...
I have a point to the story, but, does it have to end in sorrow? Can't it end happily?
I'm not sure it CAN end happily... darnit.
I just need some time to sit at the computer and type type type. I'm sure I can rely on some flow of my conscious and subconscious. I've been thinking about this story so much that I've started waking up SAYING to myself what some item needs to be in the story.
I also have quite a bit more research to do about ADD and my hometown and my past.
So, here I go. Just need to make myself sit down and type.

I think I might have ADD... because I am having such a hard time sitting down and doing one thing. I am even having a hard time sitting still Unless I'm exhausted.
I'm going to ask about it at my next doctor's appointment in a week. I hope she has an open mind. I'm tired of doctors that don't believe me.

I read pixiechick_SW's new book coming out in 2010 called, Palace Beautiful and it was a wonderful book. Really Wonderful! Of course, I can't compare her with me at all because she's written at least 3 or more books and this is my first one and we definitely write in different genres. I'm happy I got to read it before it comes out... and I will be buying a copy in 2010 and I will have her sign it. : )