It's quite clear from what we've seen so far in S2 that Jack allows Ianto to steer their relationship. It's also clear they have private discussions we're not privy to. I think it's safe to say that if Ianto had found Jack's remark to Martha that uncomfortable he would have told Jack to guard his tongue more carefully, and Jack would have done it.

I think that was Ianto's official "coming out", but I honestly doubt if anyone in the Team was in the dark about it.

As for privacy, it was just Gwen, and Gwen is "family". It's not like he said it to the whole wedding reception while toasting the bride.