I think Teddy had a much bigger hole in his life than James, but James had a bit of a complex about being the son of the Chosen One, someone he could never hope to exceed in anything except things that don't interest him much like herbology. Teddy wanted to create a horcrux to make himself invincible; his parents were killed, he'd grown up hearing stories of the martyr Fred, he didn't see any glory in death for a cause or for no reason at all. And James wanted to prove that he could do it too, though once he realized exactly what was involved, he balked.
I could have liked Tonks and Remus together if it had been based on something, anything they had in common -- bodies that transform, a passion for the Order, whatever -- but as far as I can see, she was just desperate to be luuuurrrrrved and he spent most of his time panicking and running away from her! (GAY GAY GAY oops.)