About handling dissociative tendencies and getting close to your partner/ physical contact

Not sure if NSFW. Yes, maybe. It's about physical contact and sex. So if you don't want that, please skip this post.

My question would be: My libido and arousal dissipate whenever I'm in physical contact with my partner for too long. Not sex, just laying close to each other. Not at first. It takes a while. It feels like stress is building up inside me.

Whenever we get close, a clock starts ticking. Over time ny skin gets less sensitive - I can feel touches but it doesn't feel good anymore. My jaw gets tense. Headaches start. Arousal dissipates. My head says: I like it being close to my partner. But my body just slams the door shut and shouts: nope, I'm out.

I don't think this is about performance anxiety or lack of communication.

I really would like to change this. But I don't know how.

Anyone here who knows this and would be ready to share his/ her own experience and how to successfully mitigate it?