I think people often make the mistaken assumption that evil characters are unable to form bonds with others. Not every evil character is a total sociopath.
Evil characters can still fall in love, have some sense of wanting their children to be happy, honor their family, befriend others with similar mundane interests that have nothing to do with conquest and power (e.g., sports, art, hunting).
Evil can be about how you regard (or disregard) those who mean nothing to you or can do nothing for you. Tywin Lannister, Darth Vader, Grendel's Mother, Tony Soprano, and Magneto are all evil characters who at times are motivated by a sense of love or connection to another person and even occasionally a lofty ideal or two. They just have no moral qualms about what they'll do to protect who and what they care about.
I would also add that its important to remember that villain, antagonist, and evil/immoral person are distinct concepts. They so frequently overlap it's easy to forget.
For us, it came to "Evil is choosing self over others." from there, we established that good aligned creatures do evil and evil aligned creatures do good, but its the sum total of actions that determine alignment. Therefore, we established that "Evil is choosing self over others in most decisions".
. . . check(I know some of you have heard it before)
Define what is "evil" in your game, be it because they worship an evil god,
. . . checkeat other races,
. . . checkperform cold blooded murder,
. . . checklack a soul,
. . . checkare undead,
. . . checkpractice slavery,
. . . checkhave no problem with mind control
. . . checkor because they are orcs,
. . . checkor that they see the seven deadly sin as a guideline for living life to the fullest.
That is my biggest rule for running evil games.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.