Spying is never the way to go. Relationships are built on trust. If your trust in your boyfriend is faltering then your relationship is faltering. I agree with Dez: before you try and spy your boyfriend or get into his phone you should have an honest and direct talk with him, face-to-face. I also agree with the importance of claiming your thoughts and feelings using "I" statements, such as "I feel..." instead of "You make me feel/think..."

Hope this works. If you need more advice feel free to PM me.