80-90's Alien kill off all humans except the male and female starring.

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The movie is released around 80's to 90's which is heavily copied from the movie Alien and Aliens. The whole movie is mainly taking place in a man-made space ship similar to Nostromo from the alien movie in outer space. (If memory serves me right the people in this space ship is traveling to earth)
I am not sure how but there is an alien on board (again my memory is a bit blurry but if I am not mistaken it looks like a mutated slug) that kills off all the crew on board one by one until the main hero and heroine remaining.
I dunno how and why these two human found out the alien is not really evil as he is only searching for something or was afraid . In the end the two humans befriend the alien and 3 of them is greeted by the presence of earth before the credit roll.

Would be really appreciated if someone can point me out which movie is this