[user104658]

The problem here is that you have someone who has been suppressing / altering their most basic personality in the workplace, and now has decided to be more open, which will have been a weight off his shoulders and allowed him to be more himself. The problem is, he has thus far been "faking" his work persona (everyone has one) and so now has no idea how to be himself, but also in "work mode"... and has gone way past the "balance point" into being inappropriate for work.

Honestly I would say as it was only a couple of months ago, it's worth giving him time to find that balance before making it "a thing"... if it carries on then it can be mentioned sensitively.