Being single doesn?t define you, it is only a part of who you are Smokin, and I am sad that you are being pigeon holed or feel you are. I am hoping my friends who are now single feel included, but what you say has made me think. Could you maybe arrange a night out when it suits you and invite them? Can you meet people during the day? It?s all easier said than done.
Re your boys, experience tells me that children let rip with their worst behaviour when they are at home and feeling most secure. Is DS1 behaving like this when he?s at school? If he is then I am sure they are working with you, but if not, then this is a positive sign in some ways. I bet if you posted on a behaviour thread on MN, you would get some very positive responses - by that I mean mums going through exactly what you are, so that you don?t feel the only one who has ever had to put up with this. But he is absolutely not allowed to do any of this to you. Ideas for strategies are all very well and good, but it must be so much harder without back up, but again I?m sure people with experience will be very helpful.
I really would go and pick their brains, you potentially have a lot to gain. You are a good mum Smokin, and I know that because you care so.
In my position in my school, I would be absolutely livid if a parent behaved as this snotty woman has towards you in the playground. She has no right to do that and has put herself firmly in the wrong. I would be pulling her in ?for a chat? because her behaviour is totally unacceptable. If parents have concerns about other children they go through the school.
Her notion of what has gone on is most likely based on here-say, i.e. what her child has told her, she is therefore speculating, and speculation is a dangerous thing. It is also reliant on a fair and accurate interpretation of events by her DC. 
If it is something that has happened in school, I would be very tempted to speak to your DC2 class teacher. I always maintain with behaviour in school, that if we feel it warrants involving the family then we will definitely do that without hesitation, but the majority of incidents are all part of young children learning to be together and can easily be managed within school time, not involving the parents. This may well have been one of those times i.e. something and nothing.
I think I would advise you speak to both class teachers, I would have wanted to know both things when I was a class teacher. They may well be able to give you a better perspective on things, at least give you the facts. You want to know how DC1 is getting on , particularly with regard to his behaviour in class and in the playground, and with DS2, you are keen to know what is going on because a parent has made unsubstantiated allegations.
Don?t feel shitty though. There are snotty cows everywhere, at every school, and my advice to you with her is to keep your head high, have a line for her like
?We can?t really discuss this can we, because we weren?t there? I suggest you go a speak to Miss Whatsit.?
Or become a living playground legend and just punch her one on the nose.
But best not the latter option