I hate to be negative, because what you need is understanding support, but just be prepared. You don't know what to expect so just prepare yourself emotionally for the worst to come about the situation with the boyfriend. There's nothing wrong with being a single mother if it doesn't work out. You want this child and that is what matters the most, in my opinion.

I do hope the best for you though and hope your fears will turn out to be nothing other than fears.

My advice on telling him would to just straight out tell him. If it were me I'd say "hey, if you don't want to do it then that's your decision".