ADVICE (long story)

okay so me and this guy have been talking for over a year, and through it all we are now finally together since last week. i love him and we’re so happy, spending all the time we can together. after school, he and i planned to hang out but my best friend asked if i could take her to get food quickly before her tennis practice. of course i said yes, so it was the three of us in the car. i dropped her off after food, and he and i hung out for the afternoon. she and i were talking a little bit ago and she was being short with me and she clearly felt excluded by us. i am trying to apologize, but at the same time i don’t just want to blow off my boyfriend every single time she wants to hang out. today she asked me if i wanted to go to a party on friday, but i said no because i have plans with him and i also really don’t like parties and wouldn’t have gone anyway (i was sexually assaulted at one not too long ago). how do i go about keeping her happy. she just feels like no on really cares about her lately, because she doesn’t have a man and the rest of the people in our friend group are more focused on themselves. what’s some advice to deal with keeping her and my boyfriend happy. he’s really understanding about the whole thing, and has given me some tips for it. but please, what should i do?