Oh love 
He’s going to panic as I know he isn’t ready to be a dad yet.
Given that, unless he's a LOT younger than you, I think you'd probably be best to decide if you want to continue with the pregnancy yourself first - and then talk to him. It's absolutely up to you. As it's not a serious relationship right now and he seems quite immature, I'd presume that you're going ahead alone, decide what you'd like to do, and then see what happens. If he steps up, that's great. If he doesn't, you're prepared anyway.
If you do want to go ahead, start taking a multivitamin ASAP, and talk to your midwife unit about whether additional folic acid is a good idea - I know they recommend it to mums over 38 where I am.
In the future, when you've decided what to do, it might be a good idea to have a contraceptive check if the pill isn't working for you anymore - changing pills, or using a coil/implant, or just doubling up with condoms, to save yourself the constant worry. But you don't need to worry about that just yet.
How old are your current DC? Practically, can you make another one fit? Emotionally, do you want to?