Why does my sister never feel loved enough?

she's 19 n her whole life she argued with my parents a lot especially since my dad emotionally neglected her n we lived in a low income neighborhood in Texas so things were normalized (weed , toxic ness, abusive girls/guys ) . We now moved to Illinois in a better area but she still meets toxic guys or even if they aren’t it’s like I wouldn’t say low life but guys who she relates too. She met this guy who she related too n all and she was obsessed with him n now that he treats her well she’s now complaining about how he has kids n how it makes her feel even tho she knew before hand. Honestly if a guy were to date her it would be emotionally exhausting it’s like she complains n complains n then once loved she feels disappointed by smth they did or doesn’t feel like it’s enough.
Why does my sister never feel loved enough?
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