Everything's pretty okay in this. Art's okay, the childhood adoration thing is pretty excusable and the love triangle looks fun. I'm not really a fan of harem, but since it's a yuri harem, I'm in. The only problems I could point out is that
a) as @lenne18 pointed out, there's no "when we get older, let's get married!" promise, which disappoints me so
b) the protagonist's obliviousness. Airheadedness is fine, but to be oblivious of their friends' advances is a crime... Oh wait they're all girls........ Okay fine, it's excusable. Not even I know if my friends are making a move on me.
c) the fact that their boobs seem A LOT smaller when clothed.