Sure you're not horrible for that. It could be one of your basic personality majors, or it could be caused by having bad experience by trusting on wrong people, & finding yourself with broken trust, which in that case the huge percent of people turn just like this, when things like, trust & promise get broken, it gets so hard regain it. Whatever the reasons is, don't blame yourself for it. This is something people have to understand, specially in such a world today, well trusting is a real deal today & that's big disgrace for humanity that so many people turned into fakes/abusers/cons/users/players/stoned hearts/ ect . .to easily break & use the trust, so at the end those people that feel they have been used they learn to not trust by any cost or trust very hardly. So it's not your fault, always being care full is necessary.
But also the tone of expressing is important too, i can tell someone that i don't trust them yet, but respectfully & without accusing roughly. So i hope you check that out to make sure not hurt your opposition, specially for people closer to you, the expectation of closer people might be higher cause you know them more already but yet by knowing you & who/how you are, it should make sense to them to not get upset & get along with your will about the trust issue.
But in general, it's understandable & people need to understand it,myself, I always say for even the closest person that you trust on them like your eyes, trust 99 %, keep 1 % for the possibility of their sudden changes or anything out of the blue. & doesn't matter what happens, trust gonna be earned automatically, i am sure your issue (whatever the reason is behind it) at the end depends on your feelings, the instinct & comfort zone that you are waiting to reach to make sure you can trust, whoever cross the line & don't let you proceed your comfort process, you'll never trust them, so it's up them if they understand you. Nothing wrong with you.
