Pearl isn't necessarily a bad person. She's not very nice granted but I think thats partly because life didn't turn out how she planned.
What we know about her is that she and Lester have been dating since High school. She may or may not have cheater on Lester with Sam (Sam could have just said that to upset Lester). She loves inspirational quotes and filled her home with them. She had no children.
At some point I think she regretted getting married to Lester. Perhaps because she changed or because she wanted more from life. It could be because he stayed the quiet guy who got bossed around and never got a promotion at work. Maybe she thought he would grow out of it. Maybe she feel out of love.
At some point she became unhappy and she started picking on her husband. Little thing, comments about how he looked or saying he couldn't do things. These things built up and suddenly thats all there relationship was. Without realizing it Pearl shared her pain.
This is not an excuse for Lester to kill her. But it's a fairly common story. We see couples where one of them (someones it a woman and sometimes it a man) picks and picks making rude comments about the other one and finally the one being picked on snaps. Which is what I saw happen to Lester, a moment where everything got to be too much in his head and he did the wrong thing.
I think the fact that Lester hears Pearls voice when he's in their house points to the fact that he misses her and that he feels bad about what happened. I don't want this to be taken as me saying it is ok to kill your spouse if there rude to you because thats not what I feel at all.
What i want to say is I don't think Lester is pure evil but I also don't think Pearl was asking to be killed by being 'rude' to him. What should have really happened was a divorce but that boat has sailed.
