I just think the idea that there must be one great love of your life a bit unrealistic, and pointless. Like you don't rank your children, why significant others? And I wouldn't mind if any of my grandparents spoke to me of a first love, I find it hard to understand why I would care (especially in context without Jack, Rose would never have met her granddaughter's grandfather). Even if you personally don't have any grandparents with more than one spouse or kids with other people, it's quite common

Rose isn't depicted as only caring about what she can get from others, what do you mean by that?

You can love more than one person... Maybe her husband also had a first love that influenced his life in a big way.

Could she have done anything with the necklace? Didn't an insurance company pay for it?