回答
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He has been cold to me since / after we got into a fight. He hasn't replied to my messages on LINE, and hasn't even checked them.
今は喧嘩が終わった後の後の気まずい期間なので、ここは"we got into a fight" と過去形を使うのがピッタリ。
回答
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He's been cold to me since our fight. He doesn't text me back, and I haven't seen him.
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His attitude since our fight is really cold. He doesn't answer my LINE messages, and we haven't seen each other.
アジア以外の人はLINE知らないので、一般的に「text」を使いました。この「text」は動詞で、「テキストメッセージを書く・送る」という意味です。