Patty & Selma's Ill-Fated Romance: My Sister, My Homewrecker! is a comic story featured in Simpsons Comics 2.
Can it be true? Marge's sister Selma is having an affair with -- Homer?
Marge is unable to believe her ears when she hears Homer drooling and muttering Selma's name in his sleep. She is even more disbelieving when she sees Selma kissing and caressing Homer. Looking to Patty for comfort, Marge gets up the bravery to confront Homer during another date with Selma and punch his head off his shoulders... literally.
Dr. Marvin Monroe enters to explain what is happening. In order to help Selma find a truly-happy relationship, Dr. Monroe suggested that she spend time with Homer, whom he feels is the root of her problems in finding love. Naturally, Selma refused, so Dr. Monroe had an animatronic copy of Homer made for Selma to date and break up with, which she was just about to finish doing before Marge ruined the entire treatment.
Though Marge is disappointed that she caused problems for her sister, she is at least happy to know that Homer isn't cheating on her. However, he is still moaning about Selma in his sleep... specifically Selma, Alabama, where a big all-you-can-eat ribs festival is going to take place.