My ex doesn't see my son either, and IT was particularly difficult when they are younger. I remember a particular year where in the space of six months I only had 2 hours (2single hours in 6 months) where I was not at work or taking care of DS. But things get better with time.
I suppose that you are feeling sad (but hopefully now feeling better) at receiving the grades. I remember a day when I was walking to school to try to sort yet another problem of bullying and to get (or beg) for more support for DS's SEN. I was wallowing in self pity asking my self, as many other times in the previous years, why I had to deal with all that on my own.
Then, I had a sudden glimpse of the past, of my ex "taking care" of the problem and I realised that it was much worse when he was still around. We had the same problems but in addition DS and I were feeling miserable most of the time he was involved or in touch. I try to remember that every time I feel down. We may have more financial worries but we are doing much better.
I realised work is essential to our survival and well being, not only because the money but because it provides me with an environment where, from time to time, I can do things that ultimately make me feel proud of myself, and where I can have adults conversations, have a laugh and be myself and not just mum. I have to say however that I don't think single mums stay at home out of plain choice, it has taken me hundreds of applications and a lot of tears to get out of unemployment after being a SAHM for a few years. If you are looking for a job, don't give up. It is difficult juggling childcare and work but it is doable, and there is plenty of support for single parents. It is worth it (not only at present but also for the future when all those lone parent related benefit and maintenance stop because the kids have reached a certain age).
As for looking for a partner, again, if you want one, do not give up. I sometimes feel that people judge and even think, in occassions, that you are kind of a... (Fill the blank) woman just because you are looking for a partner/dating at the time they are settled down with a long term partner tending the garden, but don't pay attention to them if their marriage broke they will be doing the same, actually many people stay in rubbish relationships for years because they are afraid to be on their own. You are a step ahead of them.
Internet dating is not for the faint hearted, but if you are not working or having a very active social life, the chances of meeting someone in a hurried trip to the supermarket are practically nil 
. My advice is to take it easy and stop looking for the initial spark (we are too old and experienced to be focused in finding love at first sight). Talk to people who are nice and respectful, but also offer that in return, once you know them a bit better you can meet for a coffee or a short walk and see what develops. It took me a lot of coffee to find DBF, but ultimately, he was worth the effort.
Best of luck.