"Divorcing" Your Parnter ("Breaking Up is Hard to Do")
by David I. Schwartz

What should you do if you have been working with the same partner all semester,
but no longer wish to? It's like any "breakup" you might face as with
bandmates, significant others, friends, lovers, etc. There's no easy way, but 
some ways ARE better than others. What is the the best thing to remember? 
Speak in terms of "I" statements.

Call/talk with the person and explain in *calm* terms your reason(s) for
needing to sever the relationship. For instance, you might say, "I'm
sorry, but I need to work on my own or with another partner for the
rest of the semester."

If your soon-to-be ex-parnter asks why, avoid "you" statements. In
general, statements starting with "you are <this> and you are <that>"
encourage arguments and defensiveness because of the implied,
perceived, or directed insult. Before using a "you" statement,
consider that each of us tends to love or hate things in others that
we see reflected in ourselves. So, a "you" statement speaks of oneself.
Choose them with care....

Instead, try "I statements," such as "I want to end the partnership because
I'm not happy" or "I need a different partner to advance my CS degree,"
lessen the blow and avoid a hurtful blame-game.