If you don't travel now, you might 'live to regret it'. [=you might feel sorry or disappointed about it in the future]
We 'regret' to inform you [=we are sorry to tell you] that we have offered the job to someone else.
It is to be 'regretted' [=it is regrettable/unfortunate] that the program has lost its funding.
(..) I have yet to make. All right, fair enough. I can appreciate that. All right. First let me say, I very much regret involving you in this. This was... This entire thing was unfortunate. Unfortunate? And I apologise deeply. Thank you. (..)2009 TvShow: Breaking Bad Title: Peekaboo Season: 2 Episode 6