So my best friend recently told me that she wanted to go to a birthday party. I told her that I may not go because I will want to spend time with my SO on that weekend. (I’ll be in training for five weeks straight and only get to go home Friday night and return on Sunday morning). She got a little upset, but I don’t understand because the party is to celebrate one of her other friends birthday. Secondly we are both 24 with full time jobs, she’s single and I’m in a relationship. Idk how to really deal with her anymore, I am sooo over the constant going out and partying all of the time, but it seems that she only wants to do that, when we hang out. We have been friends for over 10 years. Does any one have any good advice for keeping the friendship. Also am I being selfish by not wanting to go out with her on that Saturday?

I apologize in advance, if this is not the correct group to post this lol.