Your thoughts and opinions on a type of relationship for my book?

It depends on the type of story you are writing! Either would work. Make sure you know who your main character is, and stick with that POV when the couple are not together. Think about how you want your story to end, and then work towards that. If it is a love story in the traditional sense it should be more the first scenario, but if you are writing something darker, with a more tragic element to it, the second scenario would work well. Just don't lose sight of your main character, the reader must be invested emotionally in him (or her) or they will lose interest.