Characters who run away with themselves

For the first time, I have encountered one of the things that famous writers talk about all the time.

My characters have developed lives of their own.

Problem with this is, it has now affected how I resolve one of the plotlines, pulling one of my three romantic plotlines towards a more "Hollywood" ending than I had originally planned.

I finally understand why films all have certain endings, the hero wins, he gets the girl, happily ever after type things.... it's hard to write characters that you care about and not see them happy.

So I know have a screenplay that is evolving as I write, in a more drastic way than I am used to... and I'm not sure what to do about it.

Still, it's only a first draft, so maybe these things will resolve themselves.

I think the best way forward is to write the characters as they appear, and see how it goes....

Anyone got any opinions?

For that matter, anyone read this?