Do you think my wife cheat on me?

im 33 yrs old and my wife is 43 , we been married for 3 yrs . i realized that my wife dont ask me for sex any more lately and im the one who wants sex with her >> even when we have sex she dont do me right .. and she covers her face when we having sex . and she wanna finish fast . and every time i come back from work , she is sleeping or busy . so what do u think ? do u think i should fallow her and watch her ? or should i divorce her