Well, we know at the end of HBP that Lupin and Tonks are an item, and this continues through DH. I know a lot of people have felt unhappy, if not positively betrayed by this. However, I'm more happy with their relationship in this book than I was at the end of HBP, when it felt a bit like a dutiful parcelling up of spare people into neat couples.
How Lupin and Tonks are portrayed in DH seems to me to be implying (or allowing you to infer) a story which I feel is fairly convincing in human terms. In almost every scene Tonks is seen as the more assertive half, who is keeping the relationship on its feet. Lupin seems shell-shocked and unsure of how to behave. I don't mean anything so crude as 'Lupin is gay, and Tonks has pressured him unwillingly into a relationship'. Not at all. Lupin is emotionally shattered, but he is doing his best to be a good partner to Tonks.
It seems to me that the scene where Harry rips into Lupin is (behind its overt meaning) Harry saying, you have to engage fully with your new family, not your dead friend and me. And Lupin subsequently does his gallant best to comply.
I don't know. If I try to set it out like this it looks crude and a bit uglier than I feel it to be. In fact I think it's a delicate and humanly plausible relationship, which would have something like a 50/50 chance of surviving if they hadn't been killed. I know people in real life who have made compromises like this, and I feel the human heart is malleable and gallant enough for all kinds of families to work out OK.