Teshuvah Was Created Before the World
For anyone who feels cut off, the Apta Rav points to the thought before creation, where the way back already existed.
The Ohev Yisroel, speaking about Chavah, describes a person who has fallen outside the life that runs through Torah and mitzvos. On his own he has no place to stand, and no way to climb back. The Rebbe's answer is that he should remember the Divine thought that came before the world. Our Sages teach that teshuvah was created before creation. Hashem looked ahead to people who would stray, and prepared the cure before the wound. So the one who returns does not climb by his own merit. He attaches himself to that earliest will, in which his return already exists, and from there brings life back down into the world. This is why, the Rebbe says, in the place where those who return stand, even completely righteous people cannot stand. Their closeness is great, but it grew out of a return.
Source: Ohev Yisroel, Bereshis (on Bereshis 3:20)
If you feel too far gone for a fresh start, take the Apta Rav at his word: your return was prepared before you were born. Today, pick one small act of coming back, such as a short davening, a sincere apology, a chapter of Tehillim or a mitzvah you had let lapse. Do not wait until you feel worthy. Say quietly, Hashem, I am returning to what You already made room for. Let that one act be your step onto the road, and let tomorrow take care of tomorrow.