Hanging out with an old friend is now awkward?

Ok, I really need to ask this question because I felt super guilty about this. Just for starters I'm in grade 9, and it's almost the end of the year. Through the year I was friends with one girl(let's call her Sarah). Me and Sarah were really close, always walks together to class, and at lunch ect. But a couple weeks ago I started to get a little bored. It was nice and hot and sunny outside, but all Sarah wanted to do was sit inside and eat. It would be just the two of us and it was getting boring because no one else wanted to sit with her(not a lot of people like her, but I'm more popular). Even the couple other people who used to eat with us stopped eating with us. I think this is because she is pretty boring, always on her phone and not socializing or anything, always wants to stay inside(she complained about how cold it is outside, but now doesn't want to go out when it is hot). She also criticizes me and a lot of other people too. She'll say my clothes don't look like a thing a 14 year old would wear, or sweetly insult me by saying I'm disorganized or wanting attention, or trying to be more popular. So, anyway, I started to hang out with another group of people about the same time. I was bored of not going outside and stuff, plus everyone there treats me with respect and they are so much fun to hang around with. We always have a good time and me and this guy like each other now. I'm having so much more fun than I did with Sarah. I have invited her to come on multiple occasions, but she always says no. She doesn't like them very much. So now, things are really awkward between Sarah and me. I try to talk to her, but it just feels strained and stuff, and I have apologized for maybe seeming like I was ignoring her, and she said it was ok, but it still feels weird. How do I make time for both of these people? Sarah is a good friend, but so are the others. Also, I have to drive her to camp for a week in July, so I don't want it to be awkward, how can I talk to her?