Such misfortune!

Today when it became dark, my friends and I sat on the grass to eat some food, putting our purses and phones beside us.  Although there were other people around us, we didn't think too much about it.  However, when we got ready to leave, we couldn't find our phones or purses!  It was then we realized that there had been two men hanging around us the entire time and, due to our carelessness, had been able to steal them.

I feel really bad because it was my idea to eat there.  If it hadn't been for me, this never would have happened.  It's past four in the morning but I still can't sleep.  My regrets are keeping me up all night.

---That's really too bad :/ I've had many things stolen from me over the years as well.  I would suggest that you try to be more descriptive when you write a story like this.  For instance, was the grass you guys were sitting on inside of a park, a college campus, or somewhere else? What did the two men who you think stole your purses look like?  What is it that you were eating? How did you get so distracted that the men were able to steal your belongings?  All of these types of descriptions help to make a story take shape and really interest the reader.  However, I did understand your whole story, which means that your English is still advanced enough to let me know what you are trying to say :D

Good job!