Do you really want to be involved with someone who is incapable of making difficult decisions in her own life because she doesn't want to hurt someone? Dragging shit like this out for extended periods of time ends up hurting the people more as the relationship stress increases. And then, they get to deal with all of that pain and loss anyway.
If he's a nice guy then why not simply say, "Look, I like you but there's something missing and this isn't working."??
Sorry, she's got one foot in each relationship and needs to put both feet in one of them up front.
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."