Hi Emily97,
Welcome to the forums and thanks for your post.
Tony WK has given you some great advice here. I'd just like to add to it -
Most hospitals have a Social Worker; I highly recommend you get in touch with one. They can help you navigate some of the tricky things that can come with negotiating custody. Your medical history is one- but instead of just writing it down it might be about accessing your files from the GP or getting a support letter written from your psychologist (assuming you have one of course).
One of the things you might want to consider is some of the issues that might pop up preventing you from getting custody. What is it about BPD that you're finding difficult right now? How can you best be there for your son despite it all? What strategies can you put in place so that he is always cared for? Maybe this means developing a support plan for when you're feeling unwell, or recruiting more people on your side like psychologists, psychiatrists, GP's or mental health nurses so that you're not feeling alone. How old is your son? If he's at school it might be about liaising with the teachers and school counsellors there so that they can look out for him there and identify when he's not himself - i.e. struggling at school because of what's happening at home.
I also support what Tony WK said about getting things in writing; but not just visiting issues - any contact that you have with your partner from here on in. A notebook might be helpful, or even just on your phone. Calls, emails etc. This can help show that you're taking control and being proactive, organised and responsible. Even though it may seem silly at first all these little things can definitely add up later.
This website might also be helpful - www.familylawmattersaustralia.com.au
