That is a real shame your parents are acting that way. I truly wish you the best. My best advice is to keep a level head. Know what you want and focus on the strategy even if you don't see any immediate results. I've always been critical of the family unit in general in our society because so many parents and relatives (regardless of family) are selfish and ignorant. The selfish ones pretend to know and do what is best for their kids but ultimately think about what is best for themselves meaning how the kid(s) help them with their image, future, finances, etc. As to the ignorant part, many parents truly do seem to want to do what is best for their kids yet at the same time willfully refuse to learn anything new or change with the times.
My other advice is to do your best to become financially independent. It is hard in the current economy but it is essential. You recently posted about how you overdrafted your checking account and then later mentioned you were already out of money after buying makeup, clothes, and other stuff. The key here is to prioritize. None of those products are doing you any good now that you are having to give them away (temporarily). Most banks are charging anywhere from $25-$40 per item overdrafted which is a serious waste of money. If you can, try even working a second job or pick up hours at your current job. That may even "fool" your parents into thinking you are on the right track in their mind.
I'm not as financially independent as I would like as I screwed up some credit cards (well actually they did by hiking the rates) and occasionally have to borrow money and grab leftover food from my family. If transitioning is important to you (and me and all of us) we have to set goals and stick to them. It sounds like this friend that is inviting you to stay in September is a big help but it may only be one step in the right direction. Most friends will eventually want you to pay part of the rent and other expenses for continued tenancy. Plus, while they will be much more supportive of your transition than your parents, you still will have someone to answer to for other things.
This is why I stress financial independence so critically. I don't like people telling me what to do. Each time a parent, friend, or other person has financial control over you, you will be delayed in whatever goals you are accomplishing. It takes time but do your best. My goal ultimately is to own a home and have zero debt liability. That will take many years. I would strongly recommend for you though to get out of your parents' house as quickly as possible. Transitioning requires at least the most basic support--where you live and where you work. Try to save as much as you can so you can eventually get a place of your own. Any money that you may have spent impulsively on things you don't really need can be saved for a deposit on an apartment.
Worst case scenario, if you can't wait until September there may be group homes or shelters available if you live in a big enough city some of which cater towards GLBT people. Whatever you do, though, keep a level head with a clear goal and strategy in mind, and I wish you the best.
