From the way he kept starting and stopping, he must have something on his mind.
Tips
history
From Pu Songling's 《聊斋志异》 (Qing): 语甚凄楚,惊问之,欲言而止者再 — a character "tried to speak and stopped, repeatedly" — capturing hesitation born of painful secrets.
usage
Perfect for describing body language in writing: someone visibly pausing, mouth half-open, then swallowing the words.