Definition of Celibacy:  No marriage.  That's it.  Nothing about sex.

Definition of Chastity:  No sex outside of Church sanctioned marriage.

All people -- priests, adults, single, married, gay, straight, children, old people -- are called to be Chaste.  That means no sex outside of marriage, not even masturbation.

However, people aren't God, so they fail at such high standards, and they fail a lot especially in the masturbation part as well as the keeping sex within marriage part. Lots of singles have sex, including gay people, as well as priests.  Lots of married people also have sex with people they aren't married to.  It's all the same sin, whether a priest does it or spouse cheats on his wife.

For Catholics there is a simple remedy to the sin -- try not to do it again, and go to Confession.  That's it.  No big deal.

The sin merely provides a way for you to know that you are not God, but merely mortal. As a mortal, sometimes what seems the best you can do is a sin.  It doesn't mean you need to redifine what right and wrong are -- just to understand that you can't be right all the time.  Sin is human; it's the justification of sin that is evil, so Catholics can go to Confession regularly and they'll be fine.  It's really not worth getting hung up about.