I'm giving up on him... is that ok?

There is nothing wrong with sending him this email. You are telling him how you feel. You are telling him, how sad you are that he was not part of your life and you feel the reason was he didnt want to be in it...and also he was not a good dad which made you think he never wanted you. You are also telling him how much you love and miss him and how you wish he was in your life to share happyness in the future. I think your letter is great...you are, as you said getting it off your chest. It says it all and I wouldnt write any more emails or try to call him etc...because the ball is in his court now and it is his choice to take the next move. He should be proud of you...college degree, graduation with honors and making it on your own for three years. If he does not...well you did your best and you need to move on its HIS LOSS.