there's a lot going on here, shino lost her only family and found solace in her brothers wife, the only other person who could know her pain. somewhere along the way, the familial love for her sister (in-law) started to warp towards romantic love. she doesn't realize it yet because she's a child emotionally. Nozomi is in the same boat, she began to fall in love with the person she relied on for emotional support. nither are aware of the themselves.