OP, the worst thing you can do to yourself and to your game is to leave the table because you are afraid to lose. If you have the discipline to get up and leave, you should have the discipline to stay in the game, and consider it a practice to play deep stack.
Here is what you need to do....
Tighten up to the level of a nit/ play only fundamentally correct poker
Pay close attention to everything that is going at the table, and I mean everything, every little detail, I.e. sizings, positions, post flop tendencies, try to pick up tells , whatever little information you can gather as you're sitting on the sidelines.
If you fold, let's say QJo to a raise in MP, continue with the hand in your head and imagine what you'd do on every street if you were in the hand based on action, your opponents and board texture, your read , etc.
DO NOT get bored and start playing just because you are bored.
Fold when in a hand even if you feel like you have the best of it but it is a marginal situation. Remember you are staying to practice and build your mental confidence, not to win money.
Focus focus focus.
Gradually build up your mental confidence, and you will be on your way to greatness in deep stack poker