Why does my relationship status on Facebook keep deleting?

[Summer]

My relationship status on Facebook keeps changing from "In a relationship with..." to just in a relationship and my boyfriends status keeps changing to single. Neither one of us is changing it and it's really bothering me because I don't want his status to say single because then girls think they can have him (Not gonna happen!). Our one year is in a couple weeks and it didn't do it for the first like 3/4 of the relationship (its been on there the whole time). Why is it changing and how can I fix it?
I'm positive he's not changing it and I don't know why somebody else would change it, or who else would have his information..