Ash always takes a liking to his female companion/partner. Whether this is Misty, May, Dawn, Iris, etc., Ash always seems to like them (explains Ash's blushing sometimes) and vice versa as well.
When Ash leaves the region and has to say goodbye to said companion/partner, he still "likes" them and wishes he were still with them.
The female companion/partner's liking for Ash is displayed in Pokemon Heroes where Bianca gives him a sketch and kisses him. (However, this is up for debate, as this is either Bianca or the Latias disguised as Bianca, since she doesn't have her hat on).