I could almost even get it if this other girl somehow embarrassed him or screwed him over, and on top of that, he just wasn't into his childhood friend.
But the truth is the other girl was a passing acquaintance at best, and he actually does seem to like his childhood friend. So I'm not understanding the point of this manga. Just date her and get it over with. Any "revenge" should just be "I'll have a great relationship with my childhood friend".
I was expecting a harem where the underdog childhood friend was in a harem situation against a bunch of "hotter" girls that she had to overcome. This seems like it should be over already.
@Xoldin that's kind of scary. Do tell.