Hi!
First of all, let me start by telling you that your game is a great effort. Take it from me, a 49 y/o developer, that has always wanted to make a game since 18, but never did. You made the effort and put in the consistency that I didn't, alone, and that's hard and commendable.
Your game has a lot of good things. Neet 2D graphics, a lot of good mechanics (like the hyperspace jump), a simple yet effective research tree and as far as I could see my gameplay was bug free,
There are some less polished things, but I get your struggle. Three years in the making, by yourself, with little backing from the industry makes it hard to continue, with real life expenses, and I imagine the extra hours and missed family moments.
But there's one thing you won't have. Regret. The regret at reaching the middle of your life and you notice that you don't have the energy to pursue some of your goals anymore, like me wanting to make a video game.
And there are a lot of things that you DO have. The experience you gathered throughout all of these years.
Regarding the letter you left at Steam, I can just advise to never close a door entirely, and definitely not on an angry or frustrated note. Bad for the soul, and bad for the sales :).
Now let me list some of the things I believe can be improved, if you find the soul, or the financial soul to make a come back:
1. Make conversations clickable to speed the dialog up
2. Keep the skip option for players that wish to repeat the scenarion
3. Make autosaves (single player/Campaigns)
4. Make scenario checkpoints in the campaign - I recently went through the prologue and after losing, without saving, I was forced to do it all over again
5. Allow the player to do management actions, like selecting research, in the other parties turn
6. Allow to regulate the combat speed while on the other's turn.
These are some niceties that will make the game more enjoyable.
I get it, it's unlikely you'll touch it again, but keep it in mind for your next project, whether alone, or at a gaming company. The user wants story, but also the right to skip of fast-forward, and a safety net (auto-saves).
There was a game I stopped playing because of the lack of autosaves, which was an rts/crpg game and I loved it. I loved it so much that I would go half a day without saving, and once I lost I would have lost that half a day time of play. Then I started doing a save at every turn, but it quickly became monotonous. I felt I had to save as a chore. Games are suposed to be fun and distractive. It's great to have a good challenge, but it's greater to make the time we spend on it really count if you know what I mean.
Anyway, I don't want to take longer than necessary.
Thanks.
Paulo