Which point of view presents the thoughts and feelings of only one character?
first person
second person
third-person omniscient
third-person limited

I would answer first person or third person omniscient

Second person, no, because it'a a secondary character, I think

Third person omniscient is correct as well because he knows every thing about the main character and is able to write about all the facets
Third person omniscient is commonly used in stories with many characters

Third-person limited only knows the main character, so it's not enough to be able to write about feelings

I really have a doubt between first person and third-person omniscient...

But in fact, after thinking, for only one character it should be First person.

Hope this will help you to make your own choice