what to do

so this has been a problem for a while now but me and my girlfriend have been together for a while now and i believe i have what is called “relationship anxiety” and i just be overthinking about the littlest things, i always feel like im doing something wrong, sometimes i feel paranoid if they don’t text back for a while, i constantly bring up/think that i feel as if shes gonna find someone better or lose interest.. etc. you guys get the gist. but i feel like im just not cut out for relationships and it breaks my heart cus i love this girl to fucking death but i’m just so lost. i don’t wanna ruin things, and i feel like i am going to. i just need some guidance i guess. i’m not the happiest person either, like i have shit going on in my life but i just don’t see that playing into this. so if anyone could give me tips or anything i would greatly appreciate it.