Are they aware that you're having boundary issues? You need to explain to them in an open and neutral way that you're having difficulty diverting your thoughts from them and the sessions when you're living day to day life - from there they should start working on a plan to help you feel less attached when it's appropriate.

Also - are they having no other form of contact with you outside of the sessions? I don't know whether that's already part of their plan to help you deal with this but from my experience it helps to be able to email or telephone a professional in times of greater difficulty. That too has to handled carefully though as the idea is not to feed into your current attachment issues but to navigate them.

What you're going through is very normal you just need to start tackling it as part of the overall therapeutic process. Your T is there to help you with that. Good luck.