If you observe his psychology, a person who feels that his mother's friend became a friend but had intentions of marrying his father, he would feel that maybe friendship should be kept as it is because till his mother's friendship continued with vandana he was fine but when that friendship changed and formed a relationship things messed up and he doesn't want to go through that feeling
That's why sanjh is a friend to him and doesn't want to mix up different emotions in that friendship
His thinking is pretty compartmentalised this person I'd friend,this person is brother, this person is his employer
Maybe rest rela changed
A step brother became his jaan
Maya's relationship will change to love as the story is about that and they connect due to their junoon
But friendship is the relation between his mom n vandana where he
feels he got betrayed so he would remain just friends with sanjh I feel