Ok so when I say 'never uses' he said he probably has 10 friends in there and very rarely checks it. The profile pic update ties in with me asking him about finding his profile on there so was probably for my benefit.
We've had all the deep and meaningfuls about previous relationships so I know how that one started, how serious it was (or so I thought!), how it ended and how he feels about her now, but he never mentioned that they were engaged, it's the not having told me that is irking me.
I think he might not even realise that the relationship status is visible on there.