I had 6 DC's (eldest 17, youngest 1), including 2 with ASD when I became a lone parent and it was tough. But we muddled through, somehow, I had no choice so just cracked on with it! And something must have gone well as I now have 3 fantastic adult DC's, who have done well for themselves.
10 years on, with only 3 dependent Dc's, I much prefer it, even though they are teenagers and therefore evil much of the time 
. We've had quite a tough time of it, but are very close as a result. I'm not mother of the year, but I do my best as that's all I can do. And it seems to be going well most of the time. Yes, they only have me as a parent, but also no conflict between parents to ever listen. There's only me to make the rules too which can make life easier. but then again, only me to take all the responsibility which isn't quite so great...
But, it is what it is and that's that. I'm currently doing a degree and working part time so it's not easy to fit everything in, and money is always tight. But that too has it's benefits - me studying along with DD (20) also doing a degree, and teenage DS's doing their GCSE's means we can help and motivate each other along the way.
I became a lone parent due to my ExH being abusive, so TBH, being alone with them is far preferable and in many ways much easier than it was before (except financially, but adapting to a lower income was easier than I thought too). I realise my situation must feel very different for people who lost a much loved DH/ partner and father to their DC's.
But really, like others said, it's a case of having to. It can be very hard yes, but there are always people much worse off, so you just do your best, and keep your fingers crossed it'll all end well!