and agree with it. There would have been affection and friendliness to the young Emma, because of Mr Knightley's character, which is that of a gentleman. Possibly the moment he realised his feelings were deeper was when a rival with property and wealth to offer her arrived, Mr Knightley got in touch with what he really felt. This had not happened before, it was not seriously thought of that Emma might marry one day, before FC came on the scene.

Below may be an interesting other reason why Mr Knightley constantly came to visit, a small thing but I think it shows his natural personality, showing he was very much "in like" with the Woodhouses, and indeed, they were closely bound for a long time, in a country town like Highbury. There is almost a dependence there, as Mr Woodhouse's state of health makes him quite fearful and fretful. Knowing Mr Knightley, he would see this and represent the male kind of protector (hence the name!)in the community, as with his other responsibilities, especially to the older gent. In some ways, I think he would see it as a duty, and one that was probably made more enjoyable because of Emma's quick mind and spirit.

CH.55: "***In this state of suspense they were befriended, not by any sudden illumination of Mr. Woodhouse's mind, or any wonderful change of his nervous system, but by the operation of the same system in another way. Mrs. Weston's poultry-house was robbed one night of all her turkies -- evidently by the ingenuity of man. Other poultry-yards in the neighbourhood also suffered. **Pilfering was housebreaking to Mr. Woodhouse's fears. He was very uneasy; and but for the sense of his son-in-law's protection**, would have been under wretched alarm every night of his life. The strength, resolution, and presence of mind of the Mr. Knightleys, commanded his fullest dependance. **While either of them protected him and his, Hartfield was safe**. But Mr. John Knightley must be in London again by the end of the first week in November.***"

So even after John goes, Mr Knightley is still in that role. It's vital that a male can come in and protect the frail elder, nervous gentleman, and his earlier house of women. Once Emma is alone with her father, Isabella has married and Miss Taylor has married, his fears seem to increase. So it's probably even more vital that Mr Knightley be ever present in more recent years, even to the extent of living with them in the future. It's easy to underestimate what it may have been like for Emma, and very gentlemanly and right that Mr Knightley would be sensitive to it since she lost her mother.