What makes you think you won't be able to make your baby happy? All a baby really wants and needs is the love of it's mother, they don't really notice everything else for a long time. You may think that because you are unhappy now you cannot make a baby happy but by the time it comes along you will be fine, a lot can happen in 8 months and you will find your mama bear by then.
I do think the father has a right to know too though, so take a deep breath and meet with him later in the week and have an adult conversation with him about it. For God's sake don't try to use the pregnancy as a tool to win him back if your issues are still there, but hear him out on his thoughts. If it really was just the illicit substances coming between you them maybe he'll see sense but if so, don't take him back till he's proved to you he's done with it, make him work to win you back. It will take strength on your part but it will be worth it. I know you are probably not feeling strong right now but you can do it! If he doesn't, then you are worth more than him and so is your baby, you can find a way to find your own groove. I'm sorry you don't feel you could get support from your Mum, but she may surprise you.
A baby is such a precious gift and the love they give is precious and unconditional, so much deeper than the conditional love a partner can give you, or you to them. If you wanted a baby with your partner before, well things may not be ideal now but that amazing love will still be there, maybe this baby was sent to bestow that love upon you and for you to love the deepest you ever will. I know it must be scary and I hope that things with your partner work out, but if they don't, please believe that you will be fine and your baby will bring such joy into your life, in years to come you will look back on this with a knowing smile.
I wish you all the best ,take small steps and deep breaths xxx