I think your guy keeps loved ones at arm's length because he doesn't want to be rejected. Instead of making time for you, he goes sees his son, and when you reach out to him to try and keep connected, which he should understand given he made plans two weekends in a row without you, he acts coldly. Then when you don't write back, he breaks up with you because at that point he's sweating it, wondering if you might be unhappy with him. He made the first move to break up with you before you could. What is really telling is that after a long period of silence, he texts back as though nothing has happened. He continues to keep you at arm's length because he wants to portray himself as unconcerned and not involved. If he's not invested, you can't hurt him.