Why is it that you only message me when you have a girlfriend?
「貴方はなぜ彼女が出来た時に限って毎回連絡してくるの 」は英語で Why is it that you only message me when you have a girlfriend? になります。
なにがしたいの- What are you hoping to get from me?/ What are you looking to get?/ What do you want?/ What are you playing at? 等
馬鹿男,アホ男 - idiot, aresehole/asshole
例
Why is it that this idiot only messages me when he has a girlfriend? What's he playing at?
イギリス 
