If you've watched all the season's of Little House, you'll remember Dr. Baker's story from the first season. That one was much better in my eyes, and it wasn't necessary to revisit that subject matter.
This time it's Isiah who's fallen in love with a younger woman. She's blind so he feels pretty safe about falling for her, I suppose. But when she has a chance at surgery, Mr. Edwards encourages her to go for it. Unfortunately, he also knows deep down that if she sees again, she will reject him.
I suppose that somewhere along the way Mr. Edwards does come back to his senses and realize that it would never work. He hasn't been very successful in the family department up to this point and doesn't want to rob such a fine lady from a happy life...
Notice that Matthew is neither seen or mentioned in this episode.