I'm so sorry to hear that you're going through all of this. I am a former cutter also. I haven't done it for a little over a year now, but the urge is still there sometimes. I understand. It's like it never reallly goes away. It's great t that you're going to thearpy, continue doing that. Maybe try telling the thearpist that the current methods aren't working, and see what he/she can do.
About the problem with your friends always unburdening on you: It seems that you maybe DO seem like you are always the strong one, therefore, people will think that everything is alright with you and you can help them with their problems. I do the same thing, but I have learned to stand up for myself and let some one know when I'm hurting. It may be hard to not be so strong at first, but if these people are your friends, they should be able to understand, reverse roles and listen to you.
Not everybody can be strong all the time. We need to be weak some times too. If you're holding all of this in, and trying to be super strong, it may make the urge to cut even greater. From a personal standpoint, it made me want to cut even more when I held everything in and didn't say how I felt inside.
I hope some of this helps, and I really hope that you are able to overcome this. You can PM me if you want.