The strong painkillers I took earlier are just beginning to kick in and I've got that most welcome drowsy 'I wanna climb into bed' feeling but, even though I can't do it justice at the moment, I don't want to leave your post unanswered.
From what you have written, your style alone shows that you are a 'normal sociable person' and, trust me on this honey, you'll never lose the ability to meet and make friends wherever you go.
The shitty things that have happened to you over the past few years are no fault of yours. Life often throws us a succession of curve balls and, as yours have been no more or less than what many others received during the same period of time, there's no reason to suppose that you have somehow become a magnet for all things negative - far from it, in fact, it sounds as if you've dealt with adversity efficiently have remained remarkably positive in the face of what was obviously a very testing time.
You've got a problem that afflicts many single parents, namely how to have an active social while dc are too young to be left alone and where there are no other relatives to provide childcare gratis if funds don't permit paying others to babysit and, of course, your difficulty is compounded by your ds's additonal needs.
As you've made the conscious and, to my mind, right decision to put your needs on the back burner in order to concentrate on your ds at what may be a critical stage in his development, your world has grown smaller.
At the present time all you can do is make the most of any opportunities that may arise locally to make new friends and don't discount any older people, many of whom may welcome the opportunity to practice their social skills over tea/supper at your place, you may meet at community based events you can take your ds to which will enable you to get to know like-minded people in your locality.
With regard to the bone weary tiredness, make sure you eat nutritiously and grab any available opportunity to get 40 quick winks, perhaps in the afternoons if you are not working.
Keep your mind active, stay in touch with current affairs, and maybe find a hobby you can enjoy at home - such as mumsnetting 
- and, instead of looking too much to the future, take pleasure in the present because it won't come again.
Look on the friend who did you a favour last year at the expense of your mental health as having done you an enormous one by cutting contact with you - should she realise the error of her ways, please resist any overtures from her to take up where you left off.
As for being your own good cop/bad cop, that's no problem - simply be kind to yourself and don't be afraid to laugh at your own absurdities; we've all got them and some have got more than others 
Future relatonships? Never fear, you'll have them and, no doubt, there'll be a special one when you least expect it.
Jeez, it's taken me so long to write this the painkillers have been and gone and by the time it's set as a response, you may have a 100 others before mine 