Chitoge, you got this! You've been the female lead all this time, after all. The 'false love' gave you so much more time with him than Kosaki, including all of the dates in the background, and he's kept you company in dark places, comforted you from lightning storms, spent your birthdays with you, played opposite you in a romantic play, worked himself to the bone to give you cherished quality time with your mother, recovered your precious ribbon... and so many other things...
There's really no other choice.
Kosaki has always been a distraction from the real love of his life that he's put everything on the line for. I feel sorry for the girl, because she is very lovely and sweet, but Raku's tastes have definitely shifted and expanded.