For myself, one of the differences between D/s and SM is precisely the emotional connection. Casual play-partners are fine for spanking and fucking, but when we play at being Master and slave then we both know it's only play. The real thing would come with learning each other, caring about each other. I feel that the slave needs to learn about the M as much as vice versa, to care about the M's wishes not just because that's what the role demands but because of who sie is and what sie means to the slave. (I'm reminded of Antoniou's comment that the perfection of slavery is anticipatory service, to do something or deliver something just before the Owner thought of commanding it.)

As for what you do when you find that that emotional connection has happened and it's a problem... in my case, when all attempts at compromise failed I left my wife, my home and my children. If you can't risk falling in that sort of love with your D/s partner, stick to casual playmates and don't spend too long with any of them. As we warn newbies in the poly scene, you can't put a condom on your heart.