This song sounds to me like she's basically saying "I'm in love with you and I always will be, but for whatever reason you just don't make feel the same way you used to...but i'm going to hold off on leaving you in the hopes that those old sparks start flying again...but I can't wait forever." She's saying it's "All his fault" because he's not the same person anymore. That doesn't necessarily mean he's become a "bad" person...just that she feels like he's changed.
This song sounds to me like she's basically saying "I'm in love with you and I always will be, but for whatever reason you just don't make feel the same way you used to...but i'm going to hold off on leaving you in the hopes that those old sparks start flying again...but I can't wait forever." She's saying it's "All his fault" because he's not the same person anymore. That doesn't necessarily mean he's become a "bad" person...just that she feels like he's changed.