Akademik

Д-368
ДУША НАРАСПАШКУ (у кого) coll NP sing only usu. subj-compl with бытье (subj: human, VPsub | with 6biTbe( var. with .у кого), or appos pres or (less often) past fixed WOl s.o. is frank, straightforward, open, unpretentious in his relations with people
X (y X-a) - душа нараспашку = X is open-hearted
(in limited contexts) X wears his heart on his sleeve X opens his heart to people.
Фамилия этого хитрого наседки была Грицай... Я, конечно, виду не показывал, что разгадал его, - напротив, был с ним душа нараспашку, лучший друг, и таким образом многое через него всё-таки сделал (Буковский 1). This cunning informers name was Gritsai____I didn't let on, of course, that I had guessed what Gritsai was. On the contrary, I pretended to open my heart to him, made him my best friend, and in that way managed to accomplish quite a bit through him (1a).

Большой русско-английский фразеологический словарь. — М.: ACT-ПРЕСС КНИГА. . 2004.