I'm so sorry you are going through this. It is very difficult and confusing to be in a relationship with someone that is within the spectrum.
If you are ready to make changes in your relationship, and have exhausted all resources to help you both live as a neurodiverse couple, then a break-up might be the most loving thing to do. Closure in any relationship is very difficult. Give yourself as much self-love as possible for getting to this point.
Basically, if you are ready to discuss with him a break-up, speaking to him in a clear and concise manner is the way to go.
Try to keep the conversation as "business like" as possible. As always, clear, concise, and strong/fixed boundaries are needed.
A little bit on boundaries--they are very important in a relationship as they express love, love of self and respect for the other person in defining what is healthy and what works towards happiness.
Just know that often, without even being aware of it, people come from a place of fear in their relationships and allow themselves to fall into roles which they are uncomfortable with, creating resentment and pain.
If you have persistently set clear and concise boundaries with your ASD partner and have felt as if the energy spent doing so has exhausted your overall emotional functioning, then it might be time to set that final closure and stick with it.
Some responses if he reacts negatively--"I'm sorry you feel that way" or "I really need for you to listen until I'm done speaking" ....again, be clear, concise and very much to the point.
Keep the conversation short and continue to set fixed boundaries. You may need to repeat those boundaries several times. Make sure that you plan strategically, especially what to say. You may want to write everything down and practice.
Additionally, make sure to give him enough time to plan for a "serious conversation." As you are more than likely aware, spur of the moment conversations will not work. Set a good time and place to talk. A time when he is not overstimulated, tired, hungry, or possibly overwhelmed. Remain confident in your decision to leave without giving him any room to keep you dependent on his overall wellbeing.
Feel free to reach out if you need any further help and/or care. I'm a clinical psychologist in private practice that works with neurodiverse couples (ASD, ADHD, BPD).
Make sure that you work on your own self-care and self-esteem. Setting up a good support system with trusted others is key. Wish you the best.
Dr. Stella Fernandez