bah, forgot the rule that gosto usually has a 'de' or 'do' around it (sometimes even in front of it)
when do you use "do/dela/deles/etc" instead of "de" after gosta?
Why is "teu relógio" wrong?
It is also right.
No one answered an earlier question, "Why is 'teu relogio' wrong?"
When do we use "do/dos/da/das/dela/deles" in a sentence?
Why is "Eu gosto do relógio seu" wrong? But not "eu gosto relógio dele" ?
"Eu gosto do seu relógio" is what a native speaker would say...
also remember that dele means 'of him', and there is no corresponding 'of' in the 'seu' example you give above. 'seu' means his/her/their/your on its own without 'de'.
Do i have to say do? If you use "teu"or "seu" it is already good right?
The preposition is mandatory here, but you can use "De" also.