To determine your tax residency for the US, you must pass the substantial presence test. It has nothing to do with whether or not you intend to return to your home country. You must have passed the 183 day test. You must file a nonresident US tax return for 2018.
You will be considered a United States resident for tax purposes if you meet the substantial presence test for the calendar year. To meet this test, you must be physically present in the United States (U.S.) on at least:
1. 31 days during the current year, and
2. 183 days during the 3-year period that includes the current year and the 2 years immediately before that, counting:
• All the days you were present in the current year, and
• 1/3 of the days you were present in the first year before the current year, and
• 1/6 of the days you were present in the second year before the current year.
