You're not overreacting. It's quite normal to be anxious when you think about exposing this part of you to a stranger for the first time.
It's a big step, and exhausting. Take care of yourself and be aware of your anxiety. Don't deny it, but don't let it control you, either. Remember to breathe.
I just saw a new "T" today too, but he's not my first. I remember my first session with my first T was tough, but the talking comes easier with time.
Think about it like you're opening the door to let the fresh air inside.
Stay strong, brother. We're here with you.
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RIP Bryan, Life's A Dream, LAD, my little brother. I will not forget you.