How sad.... :'(
Or how happy! Maybe another way to refer to your spouse. Even if you're not each other's firsts, don't you want to be each other's posledni laska?
Why not "posledná láska"
Is it an adjective that stays in the same form, no matter the gender the noun has it refers to?
Yes, it's so called "soft" adjective.
Why is it final love but not last love?
last love is accepted as well
Why in some cases the feminine article ends in -i instead of -a? Is this another form for feminine?
'poslední' or 'posledná' or both?
only poslední, at least in Czech