Fighting with my boyfriend

So I’m a pretty insecure person and my boyfriend always says i can talk to him so when i reach out and talk about my insecurities with myself and the relationship he gets upset and immediately we start fighting.. i cant really understand why me venting about being self conscious causes him to get upset but he keeps saying things like i dont trust him or believe him. I’m basically seeking advice because these little fights or altercations seem to be coming up a lot more lately and i just wish i could find a way to stop them and stop being so insecure.