If a problem or responsibility weighs on you, it makes you worried or unhappy.

He's under huge pressure at work and it's really weighing on him. 他工作压力很大，内心负担很重。

She knew she had been unfair to him and it weighed heavily on her mind for a long time. 她知道自己以前对他很不好，这件事压在她心头已经很长时间了。