What should you do if you have been working with the same partner all semester, but no longer wish to continue the relationship? It's like any "breakup" you might face as with bandmates, significant others, friends, and lovers. There is no easy way to sever the ties, but some ways are better than others. What is the best thing to remember? Speak in terms of I-statements.
Delaying the inevitable will just worsen matters, so resolve to end the relationship as soon as possible. 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 you find such conversations difficult, you might wish to practice what you will say in advance out loud.
If your soon-to-be ex-partner 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. A you-statement speaks of oneself, so choose them with care....
Instead, try I-statements, such as saying, "I want to end the partnership because I'm not happy" or "I need a different partner to advance my CS degree," to lessen the blow and avoid a hurtful blame-game. Do not despair if you feel guilty afterwards. You are responsible for your own growth, which is painful, sometimes. Your ex-partner must also grow, so you may not only ultimately be helping yourself, but your partner as well.