Boyfriend is talking to his ex behind my back?

[Anonymous]

started with him disappearing over night , i saw him the next day asking me i'f be angry if he told me
something, I said depends what.. told me he hung out with his ex and old friends and didn't want to tell me because he was scared it would upset me, I asked if they talked even before we started dating he said no. he said they were
more friends than anything in their relationship (of 3 years) anyway. lies again about seeing her tells me 2 weeks later says all they did was "talk about movies" then asks me if he can go over and pick up all his old clothes that were left in her garage because her dad was going to throw them out i said okay sure. then a few days later he disappears for 3 days with no explanation, phones dead once he gets back tells me he freaked out because our relationship was fresh and we saw eachother too often (wich was true) and him going to her cottage was "unplanned" and he admitted to talking about our relationship to her, i saw messages when we were going camping of her saying "aw wish i could of saw u before u left" always asking him to hangout, once he said he was with me and she said what about after? (wich threw me completely
off guard) complaining about her "horrible life" and broken relationship, he constantly hides messages or deletes them when i told him billions of times i don't care if he speaks to her i just don't want him to think he has to hide it if they're friends. He kept telling me how she wants to meet me all the time and i was uncomfortable with it until i finally said sure, never met her. and recently said "Oh! so and so would like to meet you" sounding so happy, and when I looked at his messages he asked if we could all hang and she said "who's we" YES I know looking at messages is wrong, but this has been frusterating me for so long. Help.