I need dating advice?

ok so im 19 and i just started to date this girl who is 18 and i really like her ... the first day she came out with a friend while my best friend was at my place and they seemed really cool then on friday she came over and stayed the night with me (we watched twilight) and just chilled and went to bed ... she was really sweet and we had fun ... then the next day our roads were still muddy so i had to go help her with her car and i gave her another kiss and a hug again and she went home and texted me the rest of the day ... she said she wanted me to meet her parents sunday night and i said that was cool and then some how my best friend invited himself along (he likes her and its annoying) on a trip that i was to go meet her parents and hang out with her well my girlfriend told me she would pawn him off on some of her friends so we could have alone time ... well that never happend she went and got a friend and we all drove around in my girlfriends car for the night and my girlfriend stopped and told her friend to drive and she got in back with my best friend and they had a wrestling match for like 45 minutes smashing each other on the sides of her small soft top geo ... and other stuff ... then my friend made some comment and my girl friend made a comment about getting knocked up and my best friend said he didnt want kids while they were wrestling ... well the whole thing ticked me off i wanted to break my friends nose .... you know? now today my girl friend has been acting really weird and i dont know why ... i know she likes me a lot .... and i told her i wanted to break my friends nose and i didnt like that she did that and she said that she did that cuz he ticked her off .... what? .... and all of today she was acting not like she did when she did before that happend sunday night ... i dont get it? i really like this girl and i want to work something out .... i mean im tired of my best friend walkin all up on my girlfriend .... sayin hes gonna take her to victoria secret and get a show and blah blah blah ..... i know the girl likes me a lot ... i just dont get why she was acting so funny today after wrestling my friend in the car ....