A hot mess

So I'm pretty sure I'm pregnant by my ex-fiancé who has a child with someone else already. I don't think I could go through with getting an abortion and think that there should be some good thing that comes out of us not working out. I'm just scared that if I tell him about me being pregnant he'll be even more of a disappointment and I'll end up hating him and going through this alone. Any advice on whether or not I should tell him?