Never told my son about his real father

Ok, a little confused here. can you describe this again so i can understand more clearly?

Is your 17 year old son really your son, or is it this other guys?
Does this other think that he is his son?

I'm confused to on what you are asking.

It will hurt no matter what do. you know for sure it is not his son? Think about it long and hard. You son and his dad have a right to know. Most men who have raised a child would not turn their backs on the child but, he will be up set with you I'm sure. It would probly be better coming from you.

If the father doesn't know then you need to let him know now before he takes the test because if he takes the test and he is not the father and you have decivied him then you could be in a lot of trouble. If you are having issues about telling your 17 year old that the man that he thinks is his father really is not then you REALLY do need to tell him ASAP. At 17 they can get really angry about these kind of issues and the sooner you tell him the sooner the forgiving can start.

I think you should tell him
now he is old enough to move out
he wont say im runnin away to my "real" daddy when he is mad

Tell him as soon as you can! If you explain things to him the best way you can he might understand. He will probably be upset, but expect that and dont let it turn to a sreaming match, and let him know that you love him unconditionally and never want to hurt him!
Good luck

You need to tell because you want always be around and once your son starts having children then he needs to know his mother and fathers medical history in case their is something wrong with his child.He will be upset and confused but I'm sure you can explain to him why you did what you did and you both can start healing from this.

Your question is totally confusing, please re-write it & you will get good advice.

Although it may be painful to both "tell" and "hear" the truth, that is probably better than waiting even longer under this type of unhealthy stress. If your son is likely to find out anyway, sooner is better so he can deal with it and get on with his life. He is more likely to be a bit confused than angry. He just needs to know you love him very much and that you're sorry you held back the truth for so long. Don't try to give him any excuses for what you did, even if he wants to know "why." Just tell him you never felt right about keeping the secret and wanted to let him know the truth.

You should tell you son before the test. He should not find out after it is done. And he deserves to know his real father.