I don't think there should have been anything real between obi-wan and padme but perhaps the chancellor could have suggested obi-wan watch over Padme in EP III rather than Anakin, then he plays it off as if it was the council's wishes trying to distance him from her and obi-wan requested it. Then Palpatine starts to breed suspicion in Anakin by hinting at some sort of intimacy. Perhaps Anakin never knows Padme to be pregnant. He sees her and Obi-wan again for the first time since fairly early in the film and in a blind fury instantly assumes the baby (who he was never told about) is Obi-wan's. In a determination to get revenge he tosses padme aside almost killing her and calling her a "filthy whore" or (perhaps something lighter for the kiddies) and initiates the duel with Obi-wan. Yes it would be ripped off Othello but as a "tragedy" I think the prequels should have been very Shakespearean.