Facebook help needed- have i been blocked or account settings changed

Hi all,
Hoping someone can help me with my query-
I was friends with someone on Facebook, now when i go into my account, I can search for the person and go to their profile, however, all that I can see is an option to 'send a message' there is no option to add them as a friend. I can also only see their public activity.
Has the person altered their account settings and as a result all of their friends would be seeing the same thing, or have I been singled out and perhaps removed as a friend?
Any thoughts would be greatly appreciated.
Many thanks,