My first language skill is way worse after living in other countries

This is normal, sadly. It's a well known phenomenon in human language that if you aren't using the "mother tongue" frequently enough it takes a back seat, and can eventually die completely. If you didn't use it for long enough you forget almost all of it.

Crazy, right?

Totally normal

This makes sense if you are primarily using your second language daily that pushes your main language of of use because you don't use it as often as you used to.

Normal, I have a couple Mexican and Puerto Rican friends that cant speak very good spanish after they move out of their parents house. You have to continue ti use it

Funny story about language. I knew more of the Japanese language going into Japan than when I was leaving, it was so awkward to que up a conversation and the average Japanese person is too polite to correct my obviously terrible language skills.