So was the wife beating thing...

It may have just been a rumor. None of the flashbacks show him being anything hostile towards his wife.
My guess is he turned bitter after his wife died.
It's pretty common for grief to lash out as anger

I believe the wife would scream out for help when she was needing something or she was in pain from whatever disease she had (I'm assuming cancer). That's why he bought her the bell so she could summon him without screaming.

My take was that Ethan's dad beat Ethan's the mom, and the mom ran across the street to the old man's house for help. Since Ethan blamed the old man for breaking up the family unit forever, Ethan transferred the wife beater label on the old man just for spite.

The wife beater thing happened, he was being the "good neighbor" at that time.

The wife asking for help in kitchen and about door, and he was cold toward her, was BEFORE she was stricken with cancer.

When she became sick, he really started to realize what he had and was losing.

He gave her the bell to call him after death. he intended it; he tells her, almost choking up, that he will hear it when she calls.

the kid ringing the bell accidentally made him think that she was calling him.

"I'll hear it and I'll come to you."