The ground of adultery can be used where your husband or wife has had sexual intercourse with someone else of the opposite sex (so if your husband had sex with a man this does not count as adultery). It must be actual sexual intercourse - not just a kiss or 'heavy petting'.
If you decide to file for divorce on grounds of adultery, you must do so within six months of discovering that your spouse cheated on you. However, you cannot give adultery as a reason if you lived together as a couple for 6 months after you found out about it.
You can only use the ground of adultery if you are the 'innocent' party (i.e. your husband or wife slept with someone else - not if you committed adultery). However, if you both had sexual relationships with other people, either husband or wife can file for divorce.