How do you breakup with a friend you'll be in close proximity with?

There's this girl. We're not really close but we're kinda friends because we have all the same courses at college. But I can't do this kinda-friendship anymore. We often do group projects together (because we don't know any other people) and I always end up doing all the work alone.

She's really negative and always complaining ot worrying. When she's complainig I listen and support her and when she's worried 'm always supportive and tell her "you can do it" "see, you did well" "that's great". I try to cheer her up to my best abilities but I just don't have the energy anymore, especially because she never reciprocates it.

When I'm happy about getting a B in something she just goes "that's not even that good" instead of being supportive. I just don't have the energy anymore, so I want to stop being friends.

The problem is, we have a lot of the same courses and since the group projects cover the whole semester we'll be doing group projects together for another month.

How can I end the friendship when we'll still be seeing each other all the time and doing projects together?