Trust issues

I love my boyfriend of 3 years so much but lately things really haven't been ok. He's lied to me quite a lot in the past over things that were fairly important to me, although I don't think he saw them as really big things. I don't think he's ever cheated on me but lately I can't stop tormenting myself with the idea that he might have and I wouldn't know about it because he wouldn't tell me. I can't help thinking about a while back when a girl mate of his said she had something to tell me then he told me instead. He said she was going to tell me that she was in love with him and he'd known for a year and not told me and continued being close friends with her. Now I think back I'm paranoid that she was going to say he cheated with her but he stopped her. I don't think it's fair on him but I can't stop worrying about it.

I've also started to doubt a lot of what he says is true and I check his phone secretly sometimes (which I know is a really bad thing to do but in my defence he's had secrets on his phone before). His friendships with some girl mates bother me, even though I know it's nothing more than friendship and he says these are no different to his friendships with guys, I think he must prefer the other girl to me because she's prettier than I am or seems nicer or something.

Now I'm typing this I know I just sound crazy but I really need help dealing with my trust issues because they're controlling my relationship. I haven't been cheated on in the past and my parents are great and have a good relationship so I don't know where my problems come from. I did trust my boyfriend before he lied to me the first time and with every lie since then I've trusted him less and less. The problem is partially that he's really good at lying, the only way I can tell is if I catch him out. Help me please, should I trust him? And how can I manage it? Should I talk to him or do I need to deal with this on my own?