thank you :)

"él está interesado en las artes."
-- If you mean "he is interested in arts."

¿Por que? -- Why?
porque -- because

Girl, remember that in Spanish some word has accent like the subject "he" which in Spanish is "él", of you don't put the accent over the vowel like this "el" the meaning of that word in english would be "the", and what at first was a subject ends up being an article.
And, I don't understand what you want to say with "porque el esta interesado en el arto", I mean, I don't know what is "arto". Maybe you wanted to say "harto", that means "mucho" in spanish, which in english is "a lot".
If it's like that, so the correct way to say that sentence is: "Porque él está muy interesando en él", or something.

I hope to have helped solve some doubt.

so can i say:"porque el esta interesado en el arto"? ??

El esta interesado en.