Haymitch is often drunk and surly, harsh, but on rare occasions understanding, District 12's hero is often sarcastic and unfriendly, but it is revealed in Mockingjay that, even though he doesn't say it, he loves Peeta and Katniss.
He and Katniss are on the same "wavelength" for most of the books, as he can "communicate" with Katniss by unconventional means, such as the timely deliverance of a sponsor's gift. After the war is over, Haymitch is sent to District 12 to look after Katniss, but for a long period after arriving he does not visit her, opting to stay in his house and drink. It is indicated that his relationship with Katniss and Peeta is somewhat repaired as time goes on.
Haymitch doesn't sleep at night because of nightmares pertaining to the Hunger Games. When he does sleep he always clutches a knife. Drinking is Haymitch's way of tuning out the present and the pain of his Hunger Games. His alcoholism was also prompted by the loss of his entire family shortly after he won the Games, at the hand of President Snow, due to his rebellious victory. Haymitch did not have access to his liquor while he was in District 13, as the intoxicating substance is banned. He was mostly unaffected by this after therapy, but his skin became noticeably yellower. As soon as they returned District 12, he began drinking again. When Haymitch is in withdrawal, he becomes violent, incoherent, and prone to hallucinations. (Source