hello and sorry you are having so much going on to deal with.
Well i don,t need to tell you that your g/f needs medical help to overcome her depression.
do you know when or why she got depressed as despite the disrespectful children you mention you are supporting her and she is also contributing like you are to the family home..
the children shall always play up when someone else enters their mothers life and as you also say been 5 yrs now.
how do you get on with them? have you a gotten all well with them since start of relationship with your g/f.?
I realise that its not every father that steps up to the mark with child support but has your g/f never taken legal steps to make him do so..again i realise that sometimes that is easier said than done..
this is affecting your health now and its no wonder you are depressed and i would advise you both seek councelling to support each other..you will do anything for her right !!!!
okay depression is horrible and she needs to want the help as you have asked for here..you have taken the right step to address there is a problem and you need help..good for you.
I can only see two possible ways around this situation.
1) tell your g/f you can,t do this alone now and she needs to seek help as your health and mental state is also suffering.
2) if she won,t agree to seek help or councelling of some form you need to step back and sort yourself out for your own peace of mind..
Does she have any family you can turn too that would support and talk to her if she maybe not listen too you?
you are obviously in love with her but you are only human and can only carry a load so far till your back breaks..please talk to us anytime and we shall support your g/f too if she wants..we can only listen and advise you but its an open door to a start of some help if not only for you but your g/f also.