cheating is never be right option. Regardless if you feel you’re not getting the love you need or if you feel your partner is lacking sexually in some way. There is not justification for cheating. You communicate and work out your issues with your relationship.
Then, how to know your partner was cheated ?
Maybe you'll see that's he rarely to call or chat with you, but there's clue to make sure that you was cheated
Does he rarely text or call now?
Did he say where he is right now, when you asked him?
Does he seem to shy away from you, even for an ordinary meeting?
Does someone else (your friend for example) feel a change in his attitude?
Has anyone else seen him walk intimate with other girls / guys?
Does he look like he's confused when you're out with you?
Does he ever seem nervous (but covered up) when you call in the normal time?
Does he still care about the clothes you wear?
Just a reminder that cheating is NOT a part of the ups and downs of a relationship. Neither is physically hurting your partner
So, stop for cheating !