Am I the backup friend?

I have had a friend and I would say we were close but not super till we decided to go to the same college. In high school I had a friend group with my best friends a, b, and c. My friend a and b went to different colleges and of course c and I went together. In the beginning yes I would 100% say that A and C were closer and A and I were even closer than them. Typically I’m a very closed person and it takes time for me to open up, but once college began friend A got a girlfriend which the craziness of this situation led C and I to became even closer. We would debrief constantly which turned into 24/7 texting about anything and everything. This turned into 24/7 phone calls and this behavior turned into hanging out 24/7 as well. Throughout this my friend A kind of went MIA. Her college life consumed her. She wouldn’t really respond to her hometown friends anymore, texts or calls. We got accustomed to this and grew apart some. There was nothing wrong with this because we all were just living. After my first semester friend C dropped out of college but our relationship got even stronger. Once the school year was over and summer hit he had to move to a different state to start at a brand new school and out relationship didn’t change. Still constant calling and talking. We would still keep up with A but didn’t hear much. My second year of college passed and this is when friend A finally broke up with her girlfriend. This sadness led her to cling back on to her old friends which we gladly accepted but I slowly realized I felt like I was being replaced. Daily calls between C and I slowly began to stop and information I would hear from him directly I began to hear from her. Our constant talking switched from me to her in a flash. He confided in me so much for almost two years as did I but now he barley replies and doesn’t call me anymore. He went on a trip recently out of the country and he didn’t even tell me which kind of hurt that I had to hear this from friend A.

Updates
+1 y
I forgot to mention that he once started talking to this girl which he really liked and basically stopped talking to me as well but once that fell through he ran back to talking to me which is hurtful at times because it feels like it was only because I was the one there.
Updates
+1 y
Also I’m typically the one reaching out now, texts have become quite dry and phone calls now become “oh ____ is calling me I’ll call you back” and in the past I would get a callback but now I don’t anymore
Am I the backup friend?
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