The major upside is it will be easier to prove that you have product-market fit in your own backyard, for several reasons: you know your country best, no language barrier, costs will likely be much cheaper (smaller population, lower CPCs, etc.). The main downside is you won't have the same huge upside as you would if you gained traction in the US. I would highly recommend starting in your own country if you believe that will allow you to most quickly prove that people like your product / website. This is especially the case when you need momentum ASAP. Show an up-and-to-the-right growth trajectory, even if on a relatively small scale, and use the learnings and confidence to expand into new markets (and raise money if needed).

I think the first step is to remove yourself from your current work situation since you've identified that you're on the wrong path. Obviously this can be difficult to do (financially, emotionally, etc.), but it's clearly toxic and you sound ready to do what it takes to find a better path. Get significant distance from your usual daily life -- get out of the city and into a nature, meditate, exercise, read, relax, whatever works -- and start to reflect on what you've done in life that has really energized you. Think about a time when you were totally immersed in something and before you knew it many hours had passed and it was late at night...what were you doing? You could have been building a model plane, talking to a friend about an exciting topic, playing a board game -- it could be anything. Don't prescribe answers based on what seems socially right (e.g. making money, helping others, etc.), and don't worry if some of your passions at first seem small or like they couldn't amount to a career. Conversely, what are some things you've done many times (and may be quite good at) that you would love to never do again in your life? Choose to do more of the things you enjoy and less of what you don't, which will help to figure out what type of vertical you might want to be in, and simultaneously work to understand WHY you want to start a company. You'll be much happier working in something you're passionate about even if it seems un-sexy or less lucrative than the hottest new startups in Silicon Valley.