She may be a more open person if its not like outward "damn girl you look fine" kind of flirting [obviously not to that extent ha ha]

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Life is pleasant. Death is peaceful.It's the transition
that's troublesome.   --Isaac Asimov

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No, my roommate is completely straight and my girlfriend wouldn't like the fact of being with another person anyway.
I would suggest just telling your roommate off if it's bothering you so much.

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Are you serious? lol
Telling your roommate off for something as trivial as that is f**king stupid. You have to LIVE with this person, and chances are, if you let the person know that you are not interested, she'll likely stop pursuing it, for the same reason that you shouldn't "tell her off"

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Life is pleasant. Death is peaceful.It's the transition
that's troublesome.   --Isaac Asimov

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How do you mean hitting on you, like outward flirting, or playful fun?

She may be a more open person if its not like outward "damn girl you look fine" kind of flirting [obviously not to that extent ha ha]

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Its not quite that bad though, but she is always giving me compliments about how I look and she seems to be looking at me a lot.

It could be that she is just really open, or complementing, and that she might simply be envious [?].
But then again, homosexuality, and even bisexuality, are not uncommon, so it could be that as well.

I would say, if you are uncomfortable with it, so much that it is creating stress, then talk to her about it.

As for what to say, Sorry, I haven't had this problem --thank God-- so I haven't a clue what to say that would both get the point across and not come off as accusatory, in case she isn't actually hitting on you.

Good luck

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Life is pleasant. Death is peaceful.It's the transition
that's troublesome.   --Isaac Asimov