It is because you are not yet ready, and it is completely okay to feel this way at a certain phase of your Twin Flame Journey.
After going through the Purge of my fears, especially the Dark Night of the Soul, I learned that it is much easier to deal with the inner Fears, Personal insecurities, and inner pain during the beginning phase of your Twin Flame Journey.
I say this because as you grow into your Twin Flame experience, you start to grow the Unified Energy of Oneness with your Twin Flame. I call it the “Shared Energy” because you continuously merge in energy with your Twin Flame as you progress on your Twin Flame Journey.
There is no “break” from the Twin Flame experience because whether you are running from your Twin Flame or “Chasing” them, you still feel connected to your Twin Flame in every moment of your day. Your Twin Flame’s essence becomes part of who you are once you Awaken the Love that you both feel for each other.
So this Unified energy that you share with your Twin Flame is what makes you feel sad when your Twin Flame is feeling sad and sometimes it is the reason for that extreme Bliss and Euphoria that you feel randomly.
Why I mentioned earlier that it is easier to Purge the pain that you feel within you at the beginning of your Journey because once you start feeling the “Shared Energy” with your Twin Flame, you feel every Pain strongly as before because you experience both your Twin Flame’s energy of Pain. Sometimes the stress from this combined sadness will be more intensified if you are both feeling sad at the same time at that moment.
You always feel the Live connection with your Twin Flame.
To answer your question — You are afraid of physical union with your Twin Flame because you still need time to clear any energy blockages that are getting in the way of your feelings. You must first heal yourself from within, then you will feel the energy of Oneness. Once you learn to embody that shared energy within yourself — you will feel free, and in harmony within yourself and your Twin Flame connection.
All that Fear that you are feeling right now will dissolve once you Accept to fully immerse yourself in your Twin Flame energy. Finally, you will feel attracted to your Twin Flame instead of having Fear.
Keep doing the great job that you are doing with yourself.
I will leave you with these Self-help Books for your Further inspiration.
You can also find the entire Library for all my Self-help Books here — Silvia Moon.