It does not seem like you have violated your coworker's boundaries. You have helped him through a difficult time. He seems to appreciate your support and company.

As a lady with Asperger’s, I am very aware of the challenges you have described. Unfortunately, I cannot give you much advice on how to determine and repair a relationship that involves possible stalking, since all my experiences with people obsessions have involved avoidance as a solution. My suggestions would not be appropriate for the workplace, anyway. Perhaps, you can find a way to ask if you have been intrusive or not.

If you do determine that he does feel crowded by you, I suggest backing off and giving him some space.

Does your coworker ever approach you? If not, he probably does not want a friendship outside of work.