I like my best friend!!! help?

okay soo im bi and have a best friend named Lexi...we have been spending A lot of time together lately and its making me want her more and more but ive known her since i was born...she keeps wanting to come over to stay the night but i keep telling her we are spending too much time together....but she insist on coming over and she usually does which doesn't make it easy for me...i think she is bi too but im not sure ....i don't want to ruin our friendship. what to do?