While this isn't exactly the right place for this question, I'll give my input.
First, if he had one HIV test, and it was positive, there would still be the need for a confirmation test, so there still may be a chance the test was a false positive (fingers crossed).
I'm terribly sorry for what you and your BF are going through. It sounds like more than anything a mistake, it sounds like it was somehow missed (informing him of the results). I agree with teak, there really wouldn't be any kind of reason for a doctor to withhold the test results. Like I said, someone probably dropped the ball.
Either way, I would imagine you certainly would probably be in a good position legally to pursue this further, because if indeed he is + and was not informed, then his treatment was delayed, and also, if you end up being infected, that's very unfortunate, and I would think (I'm not a legal expert by any stretch of the imagination) that the doctor/doctor's office is absolutely liable.
Try not to put the horse before the cart. I would recommend both of you seeing an infectious diseases doctor ASAP. He/she will better be able to inform you on the best way to proceed. As for the legal stuff, of course you'll have to consult a lawyer, which I also would recommend doing urgently.
As for having children, it's absolutely possible for people who are infected to have healthy children, medicine has come a long way. That's not something I would spend a lot of time worrying about right now, again, tend to your immediate concerns, which would be to confirm or rule out his infection, find out what YOUR status is, and seek legal advice.
Best to you. Good luck.
No doctor is going to withhold anyone's test result.