What do you do when your best friend changes?

So ever since my best friend got her bf she has been completely different. She seemed to have got a lil bit obnoxious, bitchy and she seems to now want to ignore me. Also what is different about her when she was going out with her bf at the time, we were suppose to have a girls night out but when she came over to pick me up she told me that her bf was waiting in the car, and technically it was me observing their date... Awkward much??? But then when they broke up, i would be a good friend by checking up on her every day to see how she was doing by calling her/texting her/fb her. She then told me how she wanted to at least be friends with benefits with this guy (which is TOTALLY not like her) and she got upset when he didnt want to. Then recently at this tennis banquet we went to (since we both are on the varsity tennis teams at our schools) she was nice to me when i first went up to her to say hi and had a convo with her then i had to leave to go to my tennis team's table, but then when i went over again to say congratulations to her (because she made all-divisions) she then said thanks, and i asked her if her school is now in division one (since my schools team is division one) she then said no, and i went oh well that sucks because i would really want to play against u and it would b so much fun. She then replied saying, "well that will never happen" and i went "what do u mean", she then went "im number one" in the bitchest tone i have ever heard in my life. and i went "well i will automatically be number 2 next year" she then used her bitchy tone when she replied to my comment saying "oh then by senior year you'll finally be number one". Then she and her friends from her school didnt really make me feel welcomed when i decided to hang out with them while my mom and hers were talk at the banquet. Now the thing that makes me upset about this is that she has NEVER been like this, and we have been playing tennis together for years and NEVER has she said anything like that. She has been completely different since her having bf (who is a wicked nice guy) and i dont know what to do! Please help!