To be honest, it’s hilarious how much focus is put on that picture, when Raku is in the background, barely noticeable to anyone but Kosaki. Raku would be hard pressed to believe he was the reason it was kept. The two boys in the foreground would be seen as far more likely.
And the ending should have been expected- the status quo must be maintained. Kosaki can’t get bold enough to give him any long-term hopes. Especially when so much is riding on him keeping Chitoge happy.
But at least, at long last, after two years of knowing each other, they finally have each other’s contact information. Just goes to show you just how glacial their progress is. This is the way. Do not expect more. Kosaki is destined to squander opportunities until it is too late, I feel. Even if they seem a good match, them ending up together is the least interesting result of this entire narrative, since they were practically setup to work at the start before Chitoge showed up. It makes far more sense, and results in far more engaging narrative, to have her continue to flounder as the titular ‘false love’ grows, and she loses her chance… all because he had a ‘fateful encounter’ with a ‘monkey girl’. And what he thought was his ideal woman ends up not mattering in the end, leaving someone like Marika who tries to fit his preferences in the lurch, as well.