I suggest talking to your T about it. If it's too hard to share all at once, you could start by just saying you have the urge to self-harm.

And your T should be a safe place to process your attachment issues, too. I say this as someone who became very attached to my marriage counselor, but we worked through it. It was painful at times, but I think I've come out on the other side now and have a healthy rather than unhealthy attachment to him. If you work through the attachment issues with T, it could help you understand where the need/pain is coming from. And that could ultimately help you with other relationships in your life.