I think Harry was pretty justified in his anger at Lupin. I don't know... I'm still sorting out how I feel about Lupin's character development in DH. Remus used to be my second favorite character, but I think I'll need to read DH a few more times before I decide if that still holds. It seemed like for most of the book Lupin was under the Imperius Curse. He definitely did not seem himself. Harry may have stepped a little over the line, but Tonks WANTED to be with Lupin... leaving her when she was pregnant would just have been cowardly. She understood what she was getting into, and she was okay with it.