What is the difference between "in this year" and "this year"?
Solution 1:
You've helped us with our thesis statements in this year.
You've helped us with our thesis statements this year.
Both sentences have the same meaning and are both fine grammatically, but by convention in is not usually used to refer to the current year, and will sound strange to native speakers. You should use sentence 2.
In is usually used for a year in the past or the future, followed by a date, such as:
The Battle of Hastings took place in the year 1066.
In the year 2050, we'll all have flying cars.