I think that perhaps the wrong question has been asked. Instead of asking if it moral/immoral for Billy to accept the money from his parents to pay for his education, maybe the question should be whether or not it's ethical ?
From an ethical point of view, it would be unethical for Billy to accept the money, whilst knowingly deceiving his parents as to his sexuality.
However from a moralistic stance, is it correct for Billy's parents to deny him the funding for university based on his sexuality ? Also are his parents displaying good morals by having homophobic views. I agree they are perfectly entitled to hold them, but is it right for them to espouse them to their child ?
I also don't believe that 'coming out' is a moralistic question. It's something that can only be answered by the person in question.