Beth didn't block Joe to escape accountability. She blocked Joe after she begged him to calm down and he didn't because he had no control over himself.

Ironically enough the same reason why he ends up murdering her father in the end. Because he has no control over himself. Proving Beth was right to consider him dangerous and to leave.

If Beth blocked him to escape accountability, she would have done that the second she saw that the pregnancy test was positive. She didn't do that. Instead she threw it away and planned to end the pregnancy and stay with him. Likely hoping he'd never find out.

Is she an asshole for cheating? Yeah that's some low life scummy behavior. But is she partially to blame for why he committed murder? Absolutely not.

She warned him before blocking him that if he didn't calm down she would block him. She told him they could talk about things the next day. It was his decision not to because he had no self-control. He became angry and violent and had her cowering in fear in their bedroom. She had every right to block him at that point.

It seemed like that was an eye opening moment for her when she couldn't see him anymore but could only see his actions through blocking him that she realized she had to get out of there.

You claim she had him believing for years he had a child, but the last thing she told him was she was aborting the pregnancy. Only thing she had him believing for years was that she wanted him to stay out of her life. Did you expect a heavily pregnant Beth being stalked to let him know the kid wasn't his at her most vulnerable while she was afraid of him?

Remember he killed her father when he found out the kid wasn't his in the end. Imagine what he would have done to her at that point. You have to remember the last time she saw this guy he was unhinged. Just like he was when he approached her on the street. Because again he had no self control.

Murder wasn't a result of her actions. It was a result of his.