A male of his age, engaged in behaviors that you describe, is not acting in a developmentally appropriate way. Although there may not be actual sexual contact, what you are seeing has sexual overtones and is sometimes called emotional incest.
By our 40's we are developmentally quite fixed in how we relate to the world and others. Although it is possible that he could change, the behavior patterns that he is showing are not promising. The best way to know a person's future behavior is to explore past actions. In this case, he is unmarried, in his middle age years and is in a bonded, apparently inappropriately closely bonded relationship, with his mother.
He may genuinely have feelings for you, but until he creates a marked separation between his mother and himself he is not being realistic about those feelings, nor will it benefit you to share those feelings with him in the long run. (Unless he changes drastically)
You sound like you have made a good decision with moving on...He may be a good friend, but it appears he has a long way to go in terms of cutting bonds with his mother. Steven