relationship advice.

okay. so me & my boyfriend have been together for 5 months. and he's cheated on me a few times & ive taken him back every time  and I HATE a lier & he knows that but he has been lying to me latley. I also like to go through his phone Bc of the previous times he's cheated on me and I asked to the other day and he wouldn't let me hold his phone for anything and it got me thinking. I've felt like we've grown apart in our relationship latley and I try to get him to tell me he loves me and send me sweet little messages to reassure me but it just hasn't been helping any. can anyone help me or tell me what to do ?