Should I believe that she no longer want to be my friend?

So I have a friend we met in HS and now we are soon gonna finish college. She keeps flaking on me and the one thing that got me was she didn't invite me out to lunch for her birthday with her friends. When I asked her why she didn't invite me she's like oh I thought you were working. I haven't been working that day since January and I have told her this many times. We were supposed to hang out last week but she pushed it back and I didn't want to wait that long by myself so I said we'll schedule next time. She hasn't called to reschedule at all, she seems distant and it hurts me that she didn't even bother inviting me for her birthday. What should I do? I wanna approach her and ask her whether or not she wants to be my friend.