My boyfriend trusts me but i dont trust him

I dont trust him because he was messaging girls on Snapchat tryna meet up with them to smoke or driink thats why im psycho because he made me this way .. but he thinks im crazy and psycho… but yet he trusts me and doesnt go offf on me WHY because im loyal and dont hide anything like he does.. but why isnt he crazy with me too? Like jealous and stuff? What if i was messaging guys behind his back and cheating? He wouldnt know because he doesnt know what im doing.. but now im messaging guys too because he started it first messaging girls