Hi.
This is a tough situation for many reasons.
First, the fact that your sexual relationship with your boyfriend began two years ago may put your partner at risk for charges of statutory rape if your state sets the legal age of sexual consent as older than 16 (Most states place the legal age at 16, but about a quarter of them set it higher, at 17 or 18.).
As you consider whether or not to tell your parents, keep in mind that the situation has the potential to become pretty explosive. Your parents may feel betrayed by your decision to keep the relationship secret and feel an even greater sense of betrayal because your boyfriend is your father's friend. This anger may make them more likely to take legal action.
If you continue to see your dad's friend, you can't possibly keep the relationship a secret forever. It may be best to find a way to reveal the relationship before someone else finds out and tells your parents, or before your parents find out on their own.
If you are considering going away to college or otherwise moving out on your own, this distance may make the situation easier for your parents to accept. But don't expect a picnic--it won't be easy.
Take care.