Your honest opinion please!!!!!!!!!!!!!!!!!!!!!!!!…

ok so im actually so crazy about my girlfriend but i always have doubts over her and her flirting!!!! for valentines i got her a necklace, teddy and flowers right before she went to tunisia on holiday with football team!! when she came back she was kinda distant from me so one night i was out and my friends just piled the drinks on me..... long story short i arrived back at her place and we had an arguement. i got a little angry and stormed oout. she later texted me to say she couldnt take it anymore and broke up!!! few days later we met up.... i promised her i wouldnt drink for a long long time and we got back together. i really dont mean to sound mean now but she didnt even get me a card for valentines or even a postcard from holidays!!!! she says she loves me but sometimes its nice to get a gesture!!! she broke her phone last thurs and i went out and bought her a new one today!!! am i wasting my time on a lost cause???? she says she loves me and is mad about me all the time....... when im out she never stops texting me saying it!!! i dont get it thou. whenever she calls over to my place in college and everyones around i always catch her looking at my brother in the corner of my eye. he play for the mens version of the team she plays with now bare in mind. am i just jumping to conclusions or whats??? no mean comments... im only after advice that all!!!