I remember a woman walking to her and an alien went into her and become that lady. She later was found by another girl and she took her in and teach her to shower and actually took a shower with her. The next day the human girl went to work and her boy friend stop by and found out about the girl(alien) and had sex with her and the girl(alien) become the boy friend. When the girl(human) came back home she found that alien had transfer into the guy's body.

Sounds like "Species 2"
... The 1st "Species" was a lot better in my opinion.

No, I've seen Species and I'm 100% certain that's not it. :(

I've been wondering about the name of this movie too for a very long time. I think it came out in the early '90s, maybe the late '80s. And I remember right after she discovers the alien took her ex-boyfriend's body, some military officers arrive at her door. She tells the alien to hide, but instead he follows her to the door.

Amanda & the Alien