The Democratic party wants affordable health care for all. Obamacare was a success for many people. I'm sorry that it wasn't effective in your case. There are lots of strategies we can try to get more healthcare coverage but the essence of the problem is twofold: the cost of healthcare (which could be a lot lower) and funding for that healthcare. Both parts are complex, but the latter part involves diverting revenue used for some things into healthcare.
We can tax wealthy people more and/or we can take money used for other things and feed it into the healthcare system so that people like you can get healthcare. One of the things we might cut is our military budget, which is extremely bloated (we spend more than the next 8 countries... combined). We could also consider reducing government wastefulness (like Steve Mnuchin's $30k flight to Fort Knox to watch the eclipse on the taxpayer dime).
Please understand that Democrat proposals to make these kinds of changes are heavily resisted and therefore plans roll out incomplete (because parts were nixed during the legislative process - i.e. because you need votes and have to give up important provisions to get those votes). In some cases, programs such as Obamacare have been sabotaged by the right. Like the most recent repeal of the individual mandate, which works out well for the people who have to pay it, but is bad for the people who are receiving the healthcare funding (which comes from the tax).
The key point I am making here is that many Democrats want you to have affordable healthcare. It is important to understand who is voting for what, what provisions are nixed before the final bill, and how/why that bill is going to affect your life. Obamacare was a Democratic plan but the Democrats did not get the bill to roll out exactly as envisioned and not all states complied 100% to make Obamacare a success. Even if the bill was a complete Democrat failure, I'm sure it was not intended to be such. Sometimes, when you go in a radical new direction, there are unintended/unforeseen consequences and it can take a bit to get the kinks out.
Anyway, sorry that in this case, you suffered harm because the plan did not work well for you. I do not think that this was by design, although there are wealthy people on both sides that are not very interested in helping less fortunate people at all.
You say that you are middle-class but most people actually think they are middle-class. In truth, there is no real objective definition of "middle-class" and it's a moot point in some respects anyway because it's clear that the healthcare situation sucks for you regardless. I just want to point out that in FL, the amount of income needed to be considered "middle-class" according to some definitions is at least $30k per year with a median of around $50k: https://twocents.lifehacker.com/the-salary-required-to-be-middle-class-in-every-state-1695393156
70% of America makes less than $50k but for those that do, $300 a month for healthcare (assuming you actually can get healthcare) does not seem like an undue hardship. If you're on the lower end of the spectrum, $30k let's say, then I can see it starting to be a problem. The source of this problem is wealth inequality, where the bottom 60% of Americans only own 5% of the wealth. Like maybe some statistic says that you are middle-class but who cares if you have no actual buying power? And even in that sad state, you would still be doing better than the majority of Americans!
While at the very low end, a person might get nearly-free healthcare via a program like Medicaid (there are still small co-pays) those people makes less than $6k per year in many cases, which is considered extreme poverty. Free healthcare isn't worth much without food or housing. Food stamps only amounts to about $1.38 per meal and housing costs take up the majority of most Americans' bills (and there is almost no help with that).
My point here is that the problems are coming from the richest people at the very top, not from people doing worse than you, who may have cheaper healthcare, but can't afford a roof over their head or food. That doesn't make your problems any less real but when you look at the recent Republican tax cuts for the wealthy, you can see that this is the source of the bleeding. The government needs money to function and when the wealthy have most of the money, they need to pay most of the money. Instead, the rich vote to pay less (of course, why wouldn't they) and then make the government spend less by cutting programs that the poorest people actually need.
All of this is to say that it is really a rich vs. everyone else thing, not a Republican vs. Democrat thing, although the Democrats DO have a better track record helping the poor than the rich. You can look up voting records to verify this. You can find some information here: https://www.senate.gov/reference/common/faq/how_to_votes.htm