I think I understand this "emotional fusion" thing. Let me give it a stab:

It's when your partner's emotions are as important to you as your own. Or, at least, second guessing your partner's emotions are controlling a significant portion of your life. It's where your partner's opinion is the final judgement of your soul's worth and you're scared to death s/he'll find you wanting.

It's worse than slavery. Great songs are written about it - the one by Melissa Ethridge comes to mine:
Baby's got my heart
Baby's got my mind
And tonight the sweet devil
Sweet devil's got my soul.

"But being so attuned to your partner is supposed to be a GOOD thing."

Welcome to hell. The only one who can get you out is you.

Tom - who, to a large extent, is roasting right along with you...