Unless single motherhood is something that particularly grabs you then I would seriously consider an abortion. In addition consider that unless you're particularly attractive most if not all other guys are going to be put off getting with you. Few guys want to clean up after another guys sex life by bringing up someone else's kid.
If you got pregnant by one guy then you can get pregnant by another so better getting pregnant by a guy who is not a mental health wreck who may never get it together or go off with some other woman. Is there any chance that his mental health problems may be passed on to the baby? i.e is it genetic.
Also consider that it's a great responsibility bringing up a baby. He obviously is going to be a non starter in that so it will be all down to you. Financially I assume he has no capacity to provide and you would be looking after the kid so unless your parents, etc are willing to step in then I'm guessing it will all be living in the welfare state and that isn't great.
If there was some go in a relationship then I wouldn't usually comment as I don't like to have any sway over who gets put in this planet or not. To some extent there is no telling what will work out well and what won't in terms of people having kids but I don't think you are in a great position here and should consider an abortion particularly as it is at such an early stage.
Is there a chance that you could find a better dating prospect who you could have kids with in the future instead?