Still In Love With His Ex

I am in love with my boyfriend, who has said he is in love with me and he sounds as if he is sincere. BUT I think he is still in love with his ex, and I am afraid that he really doesn't love me. We do live together and I just wanted to know what are some signs that a guy is not over and still is in love with his ex?
I am a woman that believes that there should be trust in any relationship I am in, however trust has become an issue due to the fact that when I always mention this particular ex, whose number he still had I n his old phone and has not transferred to his Iphone, and deleted after I confronted him about it, he gives me mixed answers after I question him constantly. Ones , such as " why do you need to know," "I don't remember", and "why are you asking me this?" I really feel as though he is still in love with his ex, because a man that has nothing to hide would be honest with the woman he loves. Also what are some signs that a guy is not over his ex? Based on what I wrote, should I be worried? And why or rather what reasons would a guy not tell you about his previous relationship? I really love him and I want to make this relationship work , but this is really bothering me. I have gone through his phone before, and I am tempted to go through his Iphone. We don't talk about anything important anymore, such as his future, and mine. he doesn't ask or seem to care. I am 22 and he is 29 years old. We have known each other for 7 years now and have been through a lot. I really love him. He does ask me what's wrong, and I tell him nothing, simply because when I have spoken to him about things of a serious nature, he starts to laugh as if I don't matter, or what I am saying is not important or serious. How do you guys feel about things such as going through your partner's cellphone, or computer(when is it justified, do you feel it is wrong, and do you have a problem with it only when you have something to hide or just in general?)

*More information : We have been together since 2010, right after he was broken up with by his ex-girlfriend that same year ,via text. I have not gone through his Iphone at this moment. We are living together, and have lived together since April of this year. My boyfriend has no kids with me or his ex.) *