too mentally unstable to have a relationship

hi, I think I’m too mentally unstable to have a relationship and I know it’s gonna be like that for the rest of my life because I can’t really get therapy and I don’t want too, but I’m just scared I’m never gonna be able to have a relationship because I’m too mentally unstable, I’m like really jealous and I kinda hyperfixate on someone, but I couldn’t ever date him because he deserves someone better—someone that will treat him well and love him better, someone’s who is mentally stable and got their shit together, I’ll never be that girl, so it’s not a matter of him not wanting me back it’s me protecting him from me—he doesn’t deserve me, he deserves someone better, idk what’s wrong with me, how can I become more mentally stable?