Значение и употреба на "сe" и "cи"

[Schalksnarr]

Hey folks! I would be very grateful if you explained to me, as extensively as you like and using as many examples as you please, how and when the words "сe" and "cи" are used, and whether they have the same etymological root.

[language learner]

They are reflexive pronouns - се is accusative and си is dative. The former is used only with verbs and the latter is used with verbs and with nouns to indicate possession. E.g.:
Човекът каза името си = The man said his name.(undoubtably his own name, due to си the name can only be of the doer of the action)
Човекът каза името му = The man said his name (he could have said the name of any male person)
be prepared to meet some people that use the second sentence with the meaning of the first one. Dont use this as an excuse to not use си instead of му/й where needed though.
When the doer of the action is 1st or 2nd person, си can be replaced by ми and ти, since it's unambiguous who the doer of the action is:
Казах им името ми. = I said them my name.

Transitive verbs can take се (and си if the object is indirect) to indicate that the doer of the action is also its recipent:
Виждам масата = I see the table
Виждам се в огледалото = I see myself in the mirror
If the recipent is a part of the body of the doer, then always си is used:
Мия си ръцете = I was my hands

In addition си can mean 'to oneself'
Мисли, че положението е лошо = he thinks that the situation is bad
Мисли си разни неща = he thinks to himself(implying that he most probably dont share them) some thins
Защо говориш сам? = Why do you speak alone?
Защо си говориш сам? = Why do you speak with/to yourself?

се + verb in 3rd person singular can also be a kind of passive structure
Става се в седем часа всяка сутрин, след това се закусва = One gets up in 7 o'clock every morning, after that one has a breakfast
Звездата се вижда с невъоръжено око = The star can be seen with a naked eye.

[Schalksnarr]

Аз съм много благодарен на тебe!

When the doer of the action is 1st or 2nd person, си can be replaced by ми and ти, since it's unambiguous who the doer of the action is:
Казах им името ми. = I said them my name.

So, suppose I wanted to say "I love you with my whole being". According to your explanation, I could say:
"Oбичам теб c цялoтo ми същество" OR "Oбичам теб c цялoтo си същество", right?

[gothwolf]

I'd rather say Обичам те с цялото си същество. The first one sounds like incorrect to me because when the subject is 1st or 2nd person and the object or the attribute refers to the subject with possessive construction then I normally use the reflexive pronoun се / си.

+ It sounds more naturally to say "Обичам те" (instead of "Обичам теб"). In our speech we prefer to use the short forms of the personal pronouns. The long forms are used normally after a preposition.

[Schalksnarr]

Thank you so much, Gothwolf!