Como dizer "Eu fico sempre assim" em inglês

Dependo do contexto. Nessas duas frases:

I'm always like this (falta de contexto deixa dificil achar uma palavra exata pra "fico", mas isso funciona do mesmo jeito)
I always stay at home.

Pode mudar dependendo da frase

Eu fico com ciúmes quando voce fala com ele = I get jealous when you talk to him.

Dependo do contexto, mesmo. Com o tempo se aprende o qur usar pra certa situaçao, mas na maioria das vezes, ficar = get ou stay.

"...fica/fico sempre assim" could also be expressed with "I always get like this/get this way", as in the following sentences:

I always get like this on dates.

I'm sorry, but I always get this way sometimes. (from the song Frail State of Mind.)
“He always gets this way when the university hospital gets sued.” 
No matter how many times he watches, he always gets this way.
She always gets this way during elections.
Apparently he always gets this way every spring.
 “Oh, he always gets this way just before a race.”
 “He really is a sweet dog, but I can never let him off-leash at the dog park because he always gets this way when another dog greets him.”
My dog always gets this way. Whenever he goes out to play
He always gets this way when facing an opposing view.
But not to worry, she always gets this way before a show…
He always gets this way when he's drunk.
Oh, he always gets this way around tax time.
Katie always gets this way when she doesn't feel supported. And it gets so much worse when she's been drinking.