I definately think they are being really fake to you. Well to everyone. And you are just someone who is there when they "need" you, or need you to do something for them. You are what I call their "backup friend" a person who they dont normally hang out with, but if they dont have anyone else to do what they need then they call you. It hurts it really does but why would you want to be friends with them? They are just using you and arent really genuine. They seem genuine because they are fake, and are so good at putting on a song and dance for you. They are sweet when you see them or run into them but when your away they honestly probably do talk about you behind your back like you were saying.
I have run into so many of these women and fell for the game they were playing a few times, they are all the same. It really sounds like they are hurtful people and not worth your time or effort. I wouldnt call them or reach out to them. If they do to you then thats fine, but I wouldnt waste my energy on them. They dont seem to care what a good person you are and that you are more than that.
I would even bet that they are deep down jealous of how awesome you are and they are just mad cause they arent :)
I think that you should forget about them and go and get some friends who will appreciate you and be true friends.
Hope that you dont let them get to you too much, you arent being too sensitive.
Best wishes!