I'll say what I said to your sister: I don't like you and I definitely don't trust you, and, honestly, I don't think that's ever likely to change. But, like you said, Caroline is my best friend and the most important thing to me is that she's happy. So as long as being with you continues to make her happy then... I wish you both the best.
That being said, do not break her heart. I don't know what happened to make her trust you but, whatever it was, please don't make her regret it.