I have bad trust issues because of my past ex boyfriend, what do i do to stop doubting the boy i'm with now?

i've always had bad luck with boys, like every four of my ex boyfriends have all ended up becoming pricks and treating me badly and its caused me to have strange trust issues. and at the moment i'm dating a lovely guy, he doesn't treat me badly, sometimes he takes a while to text back to me and i worry so much when he does that because of my trust issues. with my ex he was nice to and i doubted him alot and he changed and became a prick and started to treat me badly. so i overthink things so much now and take it as a sign that the boy will change into a prick. in my mind i can already feel myself starting to doubt this boy that i am with now, and i really don't want to keep doing it because he's lovely, i like him alot, he's not immature like my exes and we get along exceptionally well. just everytime he takes an hour or two to text me back(it'll usually be for a reason never just because he can't be bothered) i get so paranoid and it gets my down and i don't know what to do or how to start being able to trust him? because i really want it to work between me and him, so my question to you is what i should do or tell myself to stop doubting him when he's not doing anything wrong... he likes me alot to and he liked me for a few months before i found out. he honestly is lovely and he's not the type of guy to like everyone so i know he's not a prick. PLEASE HELP! thank you