TL:DR; I don't know how texting with an LTR is supposed to be. Going over my conversations (I realize I played a dumb game), but also I seem very needy after afterwards.

So she's out of town for 9 days, and well, we called each other and talked the first 4 days.

On the 5th day she sent me 2 selfies, I commented that she made me smile. Then later in the day she called me as per usual (she had been initiating conversation all of this week), I didn't answer, and she wrote two messages. "Im going out soon", as to tell me "you better answer quick".

Well I didn't, I answered later around midnight instead. And she had read the messages, chosing to ignore them. I wrote a goodnight/goodmorning message around 3 in the night, I stayed up studying.

Well, the next day she was ice cold, I wrote 2 messages I believe, and she didn't check them, even though she was online (yes, pathetic that I even checked), then I tried calling as she usually answeres. She didn't. Then later around 8-9 she answered, as I was already online, and really tried to not care what her mood was, I answered, and then called after. She didn't answer.

Well at this point I probably seem quite needy, but I just try to act as if her mood doesn't affect me.

Well, today was the same, ice cold communication, just very formal writing.

I hope I've displayed my flaws quite clearly here. But I don't know how texting with an LTR is supposed to be. Should I even be bothered by her behavior? Should I act cold back towards her?

My age is 20, she is 5+ years older than me, if that helps.

Thanks in advance!