Here's an extensive tutorial on how to close a tab without a middle mouse button.
Bear with me, it's quite elaborate and technical:
The "hands-on" method (100% keyboard)
- Move the left pinky (it's usually located on the left hand) to the "Ctrl" key on the keyboard and press this key;
- While keeping this button pressed, move the left ring finger (or middle finger if you prefer) to the key marked "W" and press this key;
- You will most likely need some practice with this, as it's VERY advanced to press two keys at the same time. Just keep trying, you will get better after a while
- Computers consist of 99% magic, so this key combination will close the tab and may, or may not spawn unicorns.
The "look, I have a mouse" method (100% mouse)
- Use your (prosthetic) hand (either left or right, I don't care) to move your pointing device (mouse / pen / lightsaber) towards the "x" shaped icon of the tab you want to close;
- Left-click (or right-click depending on your orientation) on the "x" shaped icon;
- Close your eyes, because the computer needs to perform magic at this point;
- Open your eyes and behold: the tab will be closed (or a message will be prompted asking you to save your works).
Alternatively you could build a small shrine to worship the God of SublimeText and pray for the tab to be closed. This method has proven to be quirky at best and can cause spontaneous combustion of various body parts, usually depending on whether or not you registered ST2.