Answer:

The specific stanza number in Florante at Laura where Florante expresses his willingness to die for Laura is in Stanza 247:

"Ikaw na lubhang minamahal

Ay handa ng mamatay alang-alang sa iyo,

Kung hindi'y magalak ka na't ika'y sa akin ma'y sawi

At ako nama'y magdurusa't hihingi sa Diyos ng awa."

Translation:

"You whom I greatly love,

I am ready to die for you,

Otherwise, be glad and rejoice, and if you are unhappy with me,

I will suffer and ask God for mercy."