Kay - just wanted to make sure your thread didn't go unanswered. I am a single mum of one who receives child maintenance, although my relationship with my ex is not good otherwise.
I have read your Relationships thread and I feel really sorry for you. You must be feeling dreadful at the moment, very anxious about the future and the welfare of your son, and probably wishing the whole problem would just go away.
Emotionally, it must be very difficult to cope with but you're young and you have a son and, long-term, it would be worse to stick your head in the sand. If he's not treating you well and you can't trust him, leave.
www.entitledto.com is a good site where you can input the details of your financial circumstances and it will tell you what you are entitled to. I would also go to the Citiizens Advice Bureau (and possibly the lone parents advisor at the job centre) and they will talk it through with you. I'm not sure whether you work or not but you may be entitled to tax credits if you do. As a single parent, you only have to work 16 hours in order to get working tax credits and you would get child tax credits if you don't already.
If you are not working, you would get income support. I presume you would get child maintenance from your (ex-) partner (15% of his net income).
I am not the best person to advise on benefits, etc., but I'm sure someone else will help soon.
I hope you can work things out with your partner but, if he won't treat you better and you need to separate, you will be ok.