Hi Bailarina, welcome to the forum. Sorry to hear your tale of woe. I have certainly found that the dance scene, and perhaps particularly the tango scene, is beset with gossip, back-biting and shifting social undercurrents but maybe the key ingredient to coping with it lies in managing your own responses to what you find. I certainly found elements of the scene extremely difficult when I began but it eased with time.
Other people have given very good advice already, this is what I would add.
1.Don't get involved in the petty details of who said what to whom. I don't know how you know that nasty things have been said about you behind your back - ideally, avoid all situations where someone might report this kind of thing to you. What would be their motives for telling you, and how could you be sure that they have reported accurately? So much depends on interpretation - so although I feel for you as I read your account it is impossible to know from what you say what is really going on.
2.If someone puts you down openly and directly then you have the chance to deal with it in the same manner. If necessary go home, think about what you'd like to say, and have a quiet word at another time. If in doubt say nothing.
3.Remember that many people are desperately self-centred so behaviour that has cut you to the quick (such as ignoring you or "being unfriendly") may not have nearly as much significance to them as it does to you and could possibly even be accidental. People at a busy dance venue cannot possibly speak to all acquaintances each and every time so failing to greet you may not mean much - and you could pre-empt that by smiling brightly as you take the initiative in greeting them.
4. Establish your own goals and priorities and do not be deflected from them, even if this seems like a lonely path. However, do not push others aside to achieve those goals, especially other followers who will be slow to forgive.
5.Be on pleasant terms with everyone and do not get into antagonistic situations or mindsets, even with people who you feel have treated you badly or that you don't care for much. If the situation is really getting to you, walk away from it for a week or two to recover your mental equilibrium before returning to it. If you are in tears at the end of a session it would seem that this is well overdue.
6.If people gossip about you it suggests their own life seems less interesting to them than yours. Which is a kind of back-handed compliment. Also, people gossip as a means of bonding themselves into a clique, unpleasant and negative as that behaviour might seem. So you are well out of it.
7.Take compliments lightly. I can't recall the number of times someone has been complimentary about my dancing only to ignore me later, fail to recognise me or some such slight. It will drive you nuts if you let it. It's nice if someone says something nice to you but the dance world can be very shallow and it's best not to expect too much. This especially applies to teachers.
8.Look for individuals who may be on your wavelength and cultivate their friendship. There are enough lovely solo ladies on the tango scene for there to be an excellent choice. I would avoid gossipy, girly, manipulative cliques; as you rightly point out, all that should have been left behind in high school and you have the choice to rise above that kind of immature behaviour.
9.You will have good nights and bad nights. At my local milonga there are occasions when I am never off the floor and others when I am tapping my feet with frustration all night. Don't assume that leaders don't want to dance with you, maybe they are busy. Maybe they want you to ask them. Maybe they are tired. Maybe their wife needs attention. It will all turn into an agonising head-game if you let it. And the worse you feel, the more repellent you become to potential partners - it's a well-known effect!
10. Don't turn dance ability into a huge issue. It's noticeable that women who I know (or have heard

) are terrible followers are often asked to dance just as lovely followers may be sitting out. Relative ability at dancing is not important - what matters is whether you are enjoying your dancing and making progress within your own terms of reference.
11.Have faith in people's niceness. Decent people will be glad for you if you are making good progress and dance beautifully, particularly if you are very modest about your abilities. Why not? There will always be people more and less accomplished than oneself and recognising that is the route to happy self-acceptance for all of us.