I think it's a good situation to be in, it's nice to have a teacher you can be friends with. I have a teacher like that, it's great, there's like 3 of us who get on really well with her and can talk to her about anything, and go out together outside of school. It is kinda random when your teacher's talking to you about her husband and baby and everything and sometimes you are like, 'Way too much information there miss!' But at the same time it's nice she considers us people she can talk to like that, and it's cool having a natter with her about lads and a good gossip lol!
I think you always have that boundary there though, probably until quite a while after you've left school, and you won't tell them all the things you might tell your mates. However, with my teacher, I can talk to her about stuff I won't talk to anyone else about because I know she'll give good advice. It's up to the individual really. I think it's helpful to have a relationship like that with a teacher, it's really nice to be friends with them.