I don't understand the issue you're referring to with health care. Can you explain further? I also don't how being "willing" to "throw" elections helped change Democrats' opinions on gay rights? What are you referring to?
Helping a third party is counterproductive and irresponsible. The only "impact" you will make is in harming the issues you care about most. It's the same as just volunteering to help the major party you like the least. It's basically the worst thing you can do. At best, third parties in the US take advantage of well-meaning people by using magical thinking and cynicism. At worst, they're used as patsies to let foreign dictators influence the election[1].
In our first-past-the-post voting system, you have to get a majority to win, not a plurality. The party with the most votes doesn't win – the party with over half the votes wins. This means it isn't possible to have more that two competitive parties under this voting system.
I don't like that system. I think we should have a different voting system that more fairly represents people and eliminates mathematical loopholes. I also think the major political party that most closely represents my views is also the most likely to offer a chance for electoral reform.
It's a much faster, easier, and more plausible strategy to try to move the best viable party in the direction you prefer. There's effective alternatives to third parties – look at the Democratic Socialists of America or the Tea Party. These groups were able to use the major political parties to launch and implement their platform very quickly (like in one or two election cycles). There's more actual politicians aligned with groups like this than any third party, and they have massive influence over US politics. And they don't have the downside of forcing their members to shoot themselves in the foot every election.
The US absolutely needs people like you who are passionate about important issues and have the time and energy to dedicate to making real change. But please, for everyone's sake, do it in a way that doesn't directly harm the only peaceful strategy for political change that we have.
[1] https://www.nbcnews.com/politics/national-security/russians-...