It's your choice to have/not have the abortion and it's also your choice to tell/not tell him.
If you want to distance yourself from him, then if you do decide to tell him, just keep it brief like how you shared it here - "found out I was pregnant today and I've decided that I'm going to have an abortion. "
If telling him makes you feel uncomfortable in any way, then you don't have to tell him (at least not at this point). He was the one who decided he doesn't want the relationship. You don't owe him anything.
I must second RDKGames in saying that a baby can bring two people together again out of obligation, even when there are pre-existing serious relationship issues. So if you're going to have that conversation, be very wary of how it plays out. If he starts to promise to take care of you again and provide for the baby out of obligation (like you said, he's young), will it make you change your mind? You've already decided on the abortion, so make sure your heart is set right before you tell him. You can always tell him after the abortion, if you really feel the need to.
All of that being said, with regards to abortion, just make sure that this decision is what you really want. You sound mature enough to know what you're doing. Be brave, and we'll be sending you love and strength.
Best wishes.