More punctuation is needed:

"She's been really selfish and self-centred," I thought, "whereas, for me, the word 'love' is sacred and deep."

love - - > 'love'

+1

The reason for putting quotation marks around the one word ‘love’ is that the word is being referred to in a formal sense as a word or concept to be talked about. This may not be the rule in all languages, but in English it is.

Could you point out the reason why "for me" needs to be isolated by commas? Or rather, does it have to be isolated or is it only a style preference, depending on intonation or else?

The rules for English punctuation are often more difficult to explain than they are to use. I am also aware that the rules are not universal to all languages.

I think the technical term often used for this aspect of English grammar is "non-essential". That is, the sentence without the words "for me" would still be meaningful, even though the sentence is made more specific by including these two words.

A somewhat easy example of essential and non-essential might be this one:

Fred’s son, Ethan, accompanied him to New York. (i.e., Fred has only one son; the word ‘Ethan’ is added information that is not essential to understanding this sentence, so it must be set off with commas.)

Bill’s son Charles accompanied him to New York. (i.e., Bill has two or more sons; the word ‘Charles’ adds significant detail to this sentence which we would not otherwise know. That is, it was not his other son, who is named David. Because ‘Charles‘ is essential to this sentence, it is not set off with commas.)

Um..."for me" does look like significant detail, because there is a clear difference between "X is Y" (treating it as a fact) and "I think (in my opinion, for me etc.) X is Y" (treating it as a personal idea). And you certainly wouldn't put a comma if "for me" were moved to the end of the sentence.

It seems you often set off adverbial phrases at the beginning of the sentence because there is a pause between them and the rest of the sentence ("insert commas to set off expression that interrupt the sentence flow", I read), but I'm not sure there *has* to be a pause all the time. This reminds me of "though" and "too", which are comma'd optionally when at the end of sentence (at the same time, it is insisted that a comma be put before "however" even if it is in the end position, although such usage appears rather rare — I find this peculiar; is it because you are trained to always surround "however" with pauses? :>).