I really enjoyed the change of narrators. It was a great technique for illustrating just how much pain Jacob was truly experiencing. Having been involved in a similar triangle, when I was very young and oblivious to such things as "mixed signals", I was very sympathetic to both Edward and Jacob----to a lesser extent with Bella. It also gave readers an opportunity to see that Jacob was not only concerned about losing a beloved friend, or even girlfriend, but about something he considered even worse, the possibility that Edward was going to change Bella into a vampire----thereby stealing her soul.
My opinion of Leah DID change after her conversations with Jake, but some of her behavior was still inexcusable. The interest in who might be Embry's father is a good example of her bad behavior.
Yes, I think Edward did the right, and gentlemanly, thing in inviting Jake to the wedding. I understand his reasoning. If things had turned out differently, and Bella had chosed Jacob, Edward would have wanted the "choice" whether, or not, to go to the wedding. He was simply offering Jacob that same choice. I figured Jacob would show up at the wedding. He was, after all, Bella's Best Man, and it was an admirable attempt at showing support for her. Sometimes, as much as we would like to think and hope, it is not wise or prudent to maintain friendships, on the same level, after we meet our soul mate. Sometimes it's downright impossible. (In my case, I wound up breaking it off with BOTH my "best friend" and what I thought, then, was my "soul mate" AND left my poor parents to field the phone calls, from both, that went on, seemingly, forever. I cried for weeks, but I realized, like Bella, it was my own fault.)
My heart DID break for Jacob. His attempts to win Bella's heart and her soul, although youthfully exuberant and somewhat naive (remember Jake is only 16, Edward is 17 PLUS a hundred years or so), had failed. So, my empathetic heart did bleed a little-----and there are some tear stains on those pages.