That's true, I would like to see Andrew and Sarah remarry too, but Sarah seems so well-suited to being an American businesswoman and so badly suited to being royal. And I think she's well aware of that and that's no small part of the reason why they don't remarry.
As for why Sarah and Andrew's relationship is unhealthy, which I agree with, I'd say it's not so much because it's "same old same old", but because the "same old" isn't the fullest relationship anyone would wish for someone. It seems like Andrew and Sarah have a non-romantic but committed relationship with each other and romantic/sexual but non-committed relationships with other people. I don't know that this is the best of both worlds; I think the best of both worlds would be having both in one person. But as long as Andrew and Sarah refuse to move fowards, they're avoiding figuring out how to develop a committed romantic relationship with someone new, and as long as they refuse to get back together, they're avoiding figuring out what went wrong in their own marriage.
As for why Sarah and Andrew's relationship is unhealthy, which I agree with, I'd say it's not so much because it's "same old same old", but because the "same old" isn't the fullest relationship anyone would wish for someone. It seems like Andrew and Sarah have a non-romantic but committed relationship with each other and romantic/sexual but non-committed relationships with other people. I don't know that this is the best of both worlds; I think the best of both worlds would be having both in one person. But as long as Andrew and Sarah refuse to move fowards, they're avoiding figuring out how to develop a committed romantic relationship with someone new, and as long as they refuse to get back together, they're avoiding figuring out what went wrong in their own marriage.