I have talked about several things as far as your novel goes. Now let’s put it all together and call it, story line.
Your story line of course is based on your idea that you had when you saw two women talking on the street. Two women, one tall, one short. One large, one small. But really what it boils down to is the real communication you witness between the two of them.
The tall one says that her boyfriend cheats on her. The small one replies with an open mouth gasp, and the story you wanted to tell about these two women suddenly opens up a bit. So already knowing you want to write a story about two friends, this fact opens up new ideas in your head. Story line. Where do you want these two women to go? How are they connected to each other? Did they meet at work? At a party? Casually on the street? We can meet our closest friends in the most bizarre of places, and you may need to use that in your story line.
What happens in your story between these two women? Do they click at first meeting? Is there something casual that sparks their conversation? Do they like each other immediately or is it something else that brings them together?
Think about your novel the way we listen to lyrics in a song. Songs tend to tell a story in verses and repetitive chorus. There is always something about your favorite song that makes you want to listen to it over and over. Use that same analogy in your story lines.
Make your readers want to know the end of the song.