grammar - Except vs Besides

I would like to know if except and besides can mean different things in some sentences and have the same meaning in others.

For example,

1. It's hard for me to say anything to him except "hello" = Saying something that is not "hello" to him is hard for me.

It's hard for me to say anything to him besides "hello"= Saying anything more than "hello" to him is hard for me.

2. It's easy for me to trust anyone besides you = I trust you and all others easily.

It's easy for me to trust anyone except you = It's easy for me to trust anyone but not you.

It seems that when there are words that entail "negative meaning", such as impossible and hard, except and besides mean the same thing, while in other sentences, they are different.

Is this right or is there any other way to explain the difference?

What do you guys think about it?

Any opinion and advice is welcome

Thanks in advance!