The ground of adultery can be used where your spouse 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 6 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 (ie your spouse slept with someone else - not if you committed adultery). However, if you both had sexual relationships with other people, either spouse can file for divorce.