Sniper Wolf seems to love no one but herself and wolves. She's really had no one to love. But, there is someone that loves her, and that is Otacon. Otacon worked with the terrorists, but knew nothing about what they were planning. When he finds out by Snake, he is rather shocked.
Wolf was nice to Otacon, and let him feed the wolves that were there when he asked. He knew the real Sniper Wolf, he knew she wasn't a bad person. Once, he asked Snake if love can bloom, even on a battle field. Snake told him love can bloom anywhere, you just have to be able to protect the one you love.
When Wolf died, Otacon was devastated, but didn't let that eat up inside him. He wanted to help Snake, even though he killed her. He loved her, but he couldn't protect her.