My girlfriend and I have been together for about a month and her best friend tells me that she likes someone else and I don't know what to do because she is bi and it can be a guy or a girl and my friend thinks its him because he just got dumped and she's been acting weird around him and I really don't want to lose her but if she doesn't truly like me what's the point but her friend likes me so I don't know if she's trying to break us up

We don't know either. How would we?
Are you wondering what to do?
Never believe information received second hand.
When you don't know how someone is feeling about you, ASK that person.
If you aren't sure if you believe the answer, you make a decision to stay or leave.
If you don't believe the answer, you probably don't trust the person, and the relationship isn't going well anyway.
It's also possible that you are wanting answers too soon. We don't develop feelings for people all at the same speed.

Tell your girl friend what her best friend has said, and get an answer from her. If you don't believe your own girl friend, you leave. Its only been a month. How old are all of you?

If you're really concerned I would ask your girlfriend upfront about it. I wouldn't make any rash judgments off what your girlfriend's friend says especially since she's interested in you herself. She doesn't seem like a very good friend and you don't exactly know what acting weird means; there could be an explanation.

Why not just speak up and ask her.

It's possible that her best friend is just feeding you bull to try and put friction in the relationship. Don't believe what you hear unless it comes from your girlfriend's own mouth.