I went through the dating site thing too, closing the internet page down when I walked in the room etc. It drove me so crazy that I installed keyloggers on the PC and had the joy of reading his chat logs and emails. It did nothing but validate what I already knew.
Only when he stopped drinking did he find hobbies, those came before the family too, infact everything to do with him and his needs and wants came before the family.
Some people are just selfish cheats whether they're drunk or not.