Why is he like this with her?

My friend had a baby to her male friend who she was sleeping with for a few months as soon as they met. When she got pregnant, she fell for him and when she told him, he said he liked her too, but he's not the relationship type, but he wouldn't mind having some fun together.

Since he found out she liked him, he sends her dirty texts now and then when he's drunk and gets her hopes up of having some fun together, but nothing ever comes of it. They seem like good friends, get on well and he texts her everyday to ask how the baby is. But ever since they've known each other, he has never puts kisses on his texts to her, apart from when he's sending dirty texts. He puts them on all his other female friends texts and facebook messages as a friendly gesture. Also, she comments on his statuses on facebook, but he never comments on hers, even the ones about the baby.

Since having the baby, he never goes anywhere with her and the baby, even though they're both single and there's nothing to stop them. He just goes to visit them. He loves the baby to bits and says he doesn't want to ruin the friendship with my friend by sleeping together again. But he obviously treats her differently to his other friends, but why?