Anakin and Padme discuss just such in a visit from Obi-Wan in the movie and Anakin is obviously unhappy about it.Agent0028 said:In either the novelisation of ROTS or Labyrinth of Evil, can't remember which, Palpatine did make suggestions that Obi and Padme were having an affair. At one point he mentions that a Jedi was seen leaving her apartment at an unseemly hour in the morning. Which was true, but Obi was visiting Padme to make sure Anakin was okay. Personally I think that would ahve been really good to put in the movie.
And if there was still any question I'd say this exchange seals the deal:
PADME: I don't believe what I'm hearing . . . Obi-Wan was right. You've changed.
ANAKIN: I don't want to hear any more about Obi-Wan. The Jedi turned against me. Don't you turn against me.
PADME: I don't know you anymore. Anakin, you're breaking my heart. You are going down a path I cannot follow.
ANAKIN: Because of Obi-Wan?