1 and 2 need to be combined into one sentence: Yesterday i had a a farewell and welcome party with my colleagues because two new men have been assigned to my division and one of my colleagues will be stationed in indonesia in a month.
3 should be all one sentence: I usually do not drink alcohol because even a small amount of alcohol gives me a terrible headache or hangover.
During the party, the topic of our conversation somehow became about our supervisor's girlfriend.
We wanted to see her photo and asked him to show it to us.
My supervisor told me if I drank a mag of beer all at once, he'd show us the photo.
My colleagues encouraged me to chug it down.
8 and 9 are fine, but you can end 9 with a period, not an ellipsis.
Today I couldn't get out of bed because I had a terrible hangover, so I called my company to take the morning off.