Wikipedia to the rescue: Discrimination is the prejudicial and/or distinguishing treatment of an individual based on their actual or perceived membership in a certain group or category, "in a way that is worse than the way people are usually treated."
If you want the legal case, see a lawyer, but I think you'll find that you're not in any sort of a legally protected group. People who are viewed as "flight risks" (i.e., likely to leave soon) are treated differently, for better or worse, in a number of circumstances, and I haven't ever heard of that being grounds for any sort of legal action.
You do have a need to go clear the air with your boss. There's no real way to change his mind or his attitude without a private conversation. He could be mad, hurt, or have heard rumors that aren't true. It's time to fix that.
In a 1 on 1 conversation, talk honestly about where you are in the job search, and your willingness to stay with the company if you feel it suits your career. Ask him about where he sees you going in the company and in what time frame. Also see what he sees as your skill deficits and what you'd need to rise to the next level in this company - that'll tell you a lot about whether to go or stay.
Also - ask for and listen to any direct feedback in terms of your current performance on the job. It's not usual for bosses to have noticed that an employee is rarely around and on the phone/email a lot while they are doing a job hunt. That can impact negatively on your performance, whether you realize it or not, and it's perfectly valid reason for him to see you as someone who isn't dedicated.
You may not change his mind, but at least you'll be sure of where you stand. But if he's been misinformed about how quickly you are leaving, or how likely it is that you are going, this might clear up the misunderstanding.
I don't think it's wrong that you didn't tell him - most employees don't feel so comfortable giving the boss a direct heads up. But look at it from his way - he isn't going to be thrilled you're leaving, and he's not that interested in helping along the career of someone who isn't interested in sticking around.