My roommate broke up with her boyfriend

It has been four days since my roommate broke up with her boyfriend. She has beencome silent for a long time. The whole dormitory was suffused with the low pressure (This is a very weird sentence and I do not know what you mean by "low pressure". Also, "suffused" is a word that is rarely ever used and I would recommend against using it here. I don't know exactly what you meant here, but I think you maybe wanted to say, "The whole dormitory felt her sadness.") Everyone else was too careful to mention the heart-broken affair. (This means everyone mentioned the affair! I think you mean:"Everyone was careful to not mention the heart-breaking affair.")
It was her boyfriend that put forward the breakup. (This is okay, but usually people say, "It was her boyfriend that broke up with her.") My roommate didn't want to end it, so these days she tried her best to change his mind. (If you say "These days", you need an action in the present and not the past.) However, it didn't seem to work. She often cried alone when she looked back at the time she spent with him.
I cannot understand her or his feelings. In my memory, my roommate was a girl who could easily get rid of deal with such affairs. I don't know what I can do to comfort her, so I can only keep an eye on her without saying anything. I'm afraid that my words would hurt her again. I hope she could can get out of this entanglement. ("Entanglement" is a strange word to use here. I would use "situation", or instead say, "I hope she can get over this loss / heart-break.")