Why do I sabotage my own happiness whenever things go well?

Because you have quietly decided that joy is unsafe — that if you let it in, its loss will hurt more later, so you ruin it now, on your own terms. Say that fear to God plainly. Then ask for the harder courage: to receive a good thing without bracing for the blow. Joy is not a debt that will be collected. Let one good day be only a good day.

The tradition treats simcha — joy — not as luck but as something asked for and even commanded: a thing you are allowed, and sometimes obliged, to let yourself have.

From the sources “In Your presence there is fullness of joy.” — Psalm 16