I need to be quick as I've got to go out shortly to collect ds so please excuse me being brief.
Sorry to hear about how your feeling atm. Given your situation it is totally understandable.
I know of 3 people who have had breakdowns. I think it is best to seek help from a gp at the earliest possible stage. The breakdowns I've had experience of had a huge impact on the person concerned and their family. If your dp needs a wake up call then perhaps you could find out more about it and put him in the picture.
I don't know how long your dp goes to see his family (his parents you mean, I guess, as you and the children are also his family) but if it's too long and he is therefore not pulling his weight at home or is leaving you without company for too long then please tell him.
If his Mum doesn't accept your relationship then perhaps he's allowing her to get away with behaving in the way she does i.e. refusing to come to your home by going to her home twice a week. Do you think this is the case and does he?
It is really annoying when one person is doing everything and the other sits back. From personal experience I know that I've been the former and someone else has been the latter and I've thought that they, as a reasonably intelligent adult, would realise what they were doing but some people need to have the obvious pointed out, even time and time again.
Your dp needs to listen and understand and please don't let him get away with it when you ask for his help or support and he doesn't give it. Although I understand that you might feel dejected that he hasn't done what you've asked, please tell him firmly at the time and make it clear that your request was reasonable and doable and he didn't do it. Sorry, I'm rushing now because I'll have to go as soon as ds calls. (Teenagers!)
I hope that helps a little bit. You can get through this. Sometimes you need people telling you that you're not in the wrong and backing you up in order to be able to stand up for yourself. It is very hard when you feel you're being ignored.
I hope things get easier soon and that other MNers come on this thread so that you get the support MN can offer.
Sorry again to have rushed this. I hope you can make sense of it.
P.S. Did I say that I was going to be brief!