Is there anything wrong with guys taking off their shirt?

My girlfriend is acting like my mom just because i take my shirt off most of the time its not my fault im hot and have abs. so all the girls at highschool want me and they all know im in a relationship but they dont care. i keep telling my girlfriend that she is the only one that i love and that i will never cheat on her. but she has to understand that i am not some prize possestion i have a life and i need space. the other day i was at the Hospital and this nurse she is like in her 20's and i was talking to her and she told me that i have nice muscles and if i was single and my girlfriend got all in her face about it. i understand if she is jelous but there is no need for this. yesterday i had a tank top on which is still a shirt i was talking to some cheerleaders and she comes out of no where grabs my shirt, hitting me with it yelling at me to put on my shirt I mean who does that??