You know it can be so easy to say that you/you'll care.....you'll be there for someone.......you understand,,,,,,,,,,,,,,,,(and mean it!) but when something/s come up meaning you really have to "put it out there", some people just can't do that.
And it is good that you've found that out now (if that's the case). You really need people in your life who will actually care, be there, understand when it actually really matters. You deserve more!!
But she "fulfilled a purpose" in your life at the time which was fine/great (and take heart from that- it wasn't all bad!!) although now things are changing for you (along with growing up?) so now maybe it's now time to move on and find friends who are more in it for the "long haul" just the same as you would be for them.
Alison