Antecedent of pronoun "го"
What is the antecedent of the pronoun “го” in the last sentence? “Го” is masculine or neuter, but the closest noun in the preceding passage is “любов”, which is feminine.

„Един ден ти даже и без много да ме обичаш, ще жалиш много за моята любов. Това е неизбежно. Ще видиш. Ще го купя на всяка цена, даже ако е необходимо да не живея повече”.

Question

Antecedent of pronoun "го"
What is the antecedent of the pronoun “го” in the last sentence? “Го” is masculine or neuter, but the closest noun in the preceding passage is “любов”, which is feminine.

„Един ден ти даже и без много да ме обичаш, ще жалиш много за моята любов. Това е неизбежно. Ще видиш. Ще го купя на всяка цена, даже ако е необходимо да не живея повече”.

Answer

Please, let me try again: 
"го" could be "Това (което е неизбежно)" i.e. "..ти .. ще жалиш много за моята любов" or the whole first sentence as a object.  In this case the gender is neuter and the extract sounds like a warning or a threat.

Answer

As Andi said, "го" could refer to some material item, mentioned in the preceding sentences -  in the extract it's not clear about what "го" refers to.
I have found some letters of Лора to Яворов,

http://kova4ev2012.blog.bg/drugi/2014/04/01/lora-do-iavorov-pisma-ot-parij-1912.1253075
http://kova4ev2012.blog.bg/drugi/2014/04/01/lora-do-iavorov-pisma-ot-sofiia-1912.1253162

but, unfortunately the extract is from somewhere else.

As my guess only (according to the sense of the letters), it could be "щастието", but only if it had been mentioned already in the letter.
Anyway, the extract is vague about it and is not precisely quoted.

Answer

Please give next sentence :) I think it means to buy something which she like or want... because maybe he wants to prove his love ....