na-adjective, noun which may take the genitive case particle 'no'
unable to let go; stuck in the past; full of lingering attachment
Describes a person who cannot move on emotionally, often with a negative or self-critical tone. The mimetic たらたら adds a sense of dripping or oozing, implying the feeling is excessive and persistent.
彼は元カノに未練たらたらだ。
He's still hung up on his ex-girlfriend.
未練たらたらな態度はみっともないよ。
That attitude of not being able to let go is unbecoming.
未練 is the noun meaning lingering attachment or regret. 未練たらたら is an emphatic adjectival form that intensifies the sense of being unable to let go.
A mimetic adverb meaning dripping or going on and on. In 未練たらたら, it figuratively expresses that the feeling of attachment is oozing out excessively.
Compound of 未練 (lingering attachment) and the mimetic adverb たらたら (dripping, incessantly), emphasizing an excessive, persistent inability to let go.