RAHEEM STERLING admits he is obsessed. Not with neighbours Manchester United though, but more with his pursuit of becoming the best player he can. And that could spell bad news for his city rivals as they prepare to go head-to-head in tonight’s derby at the Etihad. Sterling cannot wait to be part of the fight to prove who is the top club in town when the Red Devils pitch up. But the bigger battle for him is continuing his amazing recent improvement. And he reckons playing for a top club like City means there are no excuses for him not doing so.England star Sterling, 24, said: “It’s all about mentality, maturity and growing up. “I’m obsessed with football, obsessed with scoring goals, obsessed with recovering quicker and obsessed with improving myself. “You have every facility here so you have to use it to your advantage to try and be the best you can be.” The arrival of boss Pep Guardiola at City in 2016 inspired Sterling to hit new heights — but he admitted a change in attitude has also helped.He added: “I was decisive but I wasn’t 100 per cent committed. “I wasn’t 100 per cent living the way…