Am i just being over-sensitive or is my friend completely insensitive?

So sorry to hear about your long term breakup. It's obviously very painful. At the moment you are going through a transission from the old you, to the new you. It's a painful time, and at the moment you cannot judge people from a balanced state of mind. If you do not like the way you feel when you are around this person, then you need some time alone. What has happened is that your circumstances have changed, but your friends dont fully comprehend what this means to you. Time alone will allow you to find the new, single you, and when you start changing other people will recognise this and change they way they relate to you. Good luck x