How do you always stay skinny?

I was fat growing up, then lost 30lbs, but ever since it's a cycle of gaining weight then losing them back in the last 3-4 years or so. I know how to properly lose weight through exercise (I run), but the problem is I get a new job and it's harder to go to the gym everyday and I eat out far more, then after 6 months I've gained 12 lbs before I know it. And as a former fat kid, I can really eat a lot if I want to. Getting high also gives me the munchies so that just doubles my eating capacity.I know everyone struggles with it but there's tons of young guys my age who can always stay skinny regardless of how muscular they are. Any tips? I mean quitting 420 will probably help. I just gotta get more committed to the lifestyle, but so many guys are so lean all the time and I envy. I genuinely wonder if they have a much higher activity level, or work out a lot more than I do (I run 2-3 times a week), or eat far less than I eat without knowing.I mean I know how to calorie-count and everything, but eating 1800kcal everyday is time consuming and hard. And also it's hard to not get hungry on that.