Several Sentences with New Words
1) I have to run some errands before\by the afternoon but then I'm yours.
..before noon/the afternoon, but then I'll be yours.
2)Don't you see that you can't even give me some slack? You believe I should concentrate on your goals day and night.
Correct! Maybe, You think I should be concentrating ... would be more natural.
3) They had constantly experienced irreconcilable differences until the moment he filed for divorce. He divorced her but now they look best friends.
They were always having irreconcilable difference ... He divorced her, but now they seem to be best friends/they look like best friends.
4) He goes through a real experiment and undergoes huge load, but I believe he'll get over it.
Grammatically correct, maybe experiment isn't the right word though.
5) I don't know this word, I should look it up.
Correct!
6) He was detained and put under custody. I'm afraid his destiny\fate is solitary confinement.
He was detained and put in/kept in custody. .. his fate .. (destiny is more positive than fate I think)
7) Why is your room always that messy? Do you clean it\put it in order at least once in a while?
...always so messy? Can you clean it at least once in a well?