The novels you don't write are the worlds that never will be. There are 7 billion people in this planet, and quite a few will enjoy reading them, because we are *that* diverse. Sure, some people will not like it, but others will.
And I know this, because I'm finishing my 2nd novel these days, and with the first I've seen people that like it and people that don't. And so it'll happen with you. It's thrilling to write about something even if it's just for you. The journey getting from the start to the end of the story you have in mind, getting to know your characters and your world is a very cool experience for a writer, and as others have said, for all you know, you may very well be writing the next big thing, but you won't know if you don't finish the novel (and come on, steampunk is a *very* popular genre, people will like it, and you know it!).
If you need help and you are in the US, dial up that number that others have given you, if you're not, seek help, even among your friends if you'd rather not turn to professional help, but it may be worth considering. But remember, unfortunately we all go through very dark times at some point in our lives, it can be soul crushing, but there's no reason to give up. You have loved ones, people that care for you, and even a bunch of strangers in a forum, thousands of miles away from wherever you are, encouraging to keep pushing. You're not going to give us up, are you?