You’re going to need this...
It is really, really, really hard to cook efficiently for one.
Some people do meal prep and eat the same thing day after day.
I gave up and use a service that delivers me a cooler full of dinners (not frozen) every week. Freshly would be the national equivalent, but I found their portion sizes to be too small and they use a lot of packaging. I leave a few nights empty so I can go out to dinner on a date if needed.
Even paying someone else to cook for me, the cost per meal is less than what I was spending at the grocery store after waste was accounted for.
I also don't have a dishwasher so I hate involved recipes. If you have a dishwasher, you might have luck with preportioned cooking kits like Blue Apron and the like.
If you don't want to do any of this and still want to shop at the store, I find salads to be the best way to go for scaling things up/down.
Bonus link to the world's loneliest cookbook because I love the cover: https://www.amazon.com/Microwave-Cooking-One-Marie-Smith/dp/1565546660/ref=sr_1_1?keywords=microwave+cooking+for+one&qid=1566792626&s=gateway&sr=8-1
This was a personal favorite of mine at your age.
I do, and it doesn't get anymore depressing than Microwave cooking for one! https://www.amazon.com/Microwave-Cooking-One-Marie-Smith/dp/1565546660
This looks like it's taken straight from the cover of some sad 70s (80s?) cookbook like "Microwave Cooking for One".