In Season 1, Alan and Evelyn get along better. It is Season 2 that there relationship becomes much like Charlie and Evelyn's. Evelyn has mentioned on several occasions that Alan was always the 'good son'.
In "Castrating Sheep In Montana", Evelyn tells Alan that they were through, but that didn't last long.
In "Nice to Meet You, Walden Schmidt", she tells Alan he's going to move in with her. Although she says on several occasions that he can't (After he moves back into the beach house, too; I Changed My Mind About the Milk, I Think I Banged Lucille Ball).
In "Those Fancy Japanese Toilets", Evelyn tells Alan that they were all that was left of the family. Saying, 'You were always the good son. Now, you're my only son'.
However, In "Why We Gave Up Women", A horrified by a heartattack Evelyn tells Walden, 'I already lost my good son', refurring to Charlie.
Alan and Evelyn are the only characters to be series regulars every season, Alan is the only character to appear in every episode.