How to memorize opening sidelines?

Hello, per the advice of a strong player I've decided to start studying openings starting with the QGD, namely with the Alatortsev variation. I am capable of memorizing the mainlines of these variations (the alatortsev being just one) but feel overwhelmed going over each sideline every time I review my pgn. Is there a better way to study an opening variation and its sidelines? Any advice from strong players as to how to accomplish this goal?

Here's my pgn for the Alatortsev:
Notice how there are multiple sidelines to what is already just a variant of one larger opening.
Openings grow like a tree, branching off repeatedly and I just don't know how to learn these branches in a methodical way.


TL;DR
Having trouble memorizing a growing tree of chess moves in a methodical way

You don't need to memorize opening lines just know not to blunder in the opening and basic principles. Me personally I've only memorized 5-6ish moves in the start of the opening, you don't need opening knowledge until very high elo. In 1500 just focus on improving actual chess in mid game and endgame

Understand the ideas and just play the position. If you play fairly accurately, you'll be on some line played before, maybe even with a fancy name ...

@ISOVAKO I understand where you're coming from andappreciate your reply. Perhaps it isn't necessary to memorize it to this depth. I do want to follow through with the advice I recieved from a strong player and learn a few openings to specialize in though. I think you're right that I shouldn't burden myself with learning tremendous amounts of theory, but I do want to learn some theory to become competent in the opening and its middlegame ideas. This involves learning a mainline and at least some side variations. Were I to be persistent in my goal of learning openings, would there be any advice you could give as to how I could manage to do this?

Should I cut back on the amount of variations? (probably yes) - In fact, I could pick variations which are more suitable to my style of play and discard the rest.
Should I tabulate them like in the opening books and go through them line by line? (seems like the most methodical way)

Any thing I may have missed?

Thank you again for your time and help,
(my online pseudonym) - Peter Doocy