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。
He's been cold to me since our fight. He doesn't text me back, and I haven't seen him.
His attitude since our fight is really cold. He doesn't answer my LINE messages, and we haven't seen each other.