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.
(..) there's no love in you. Because if there is... just a little bit of love in there for me... I think that in a few minutes you'll regret you never said anything. I love you, Leon. I win. I took a hit. I need a hand now. I know she's young, (..)1994 Léon: The Professional