I really need advice i foud somthing on my boyfriends phone guys and girls plzzzzzz help?

ohkay so me and my bf were talking on the phone and all of the sudden "click" so start to call him back and it kept oing straight to voicemail and one of the times straight to voicemail and one of the times it just playd his voice mails :( so stupid me lestend to them low and behold a voicemail starts to play " i dont know how u can say u never loved me....theres 5 dollers on my bed it must of fell out if your poccet, so ya bye" the voice was kim his ex girlfriend that has been trying to get him back so i lestiend to the time date and who it was from and yea it was her how do i know cus when it was saying the number of the caller it said 808....... blah blah well yea she has a huwii number and i know cus she used to call me all the time! and i confrinted my bf and he got pissed and was like thats privet so i said i dont keep anything privet form you, you know everything.....who should be more mad him or i and what should u do....could he posibly be cheating