I saw him talk about his grief without holding back ... And I let him speak ... I did not stop him ... Because grief goes away when you talk about it ... because talking about your sorrow helps you to lessen it ....

"I saw his grief eloquent" ---> I saw that he was talking eloquently (fluently) about his grief (his pain, his sadness). "and I let it have its flow" ---> and I didn't interrupt him "for sorrow relieves itself by words". (for = because , sorrow=sadness) ---> because a sad person can ease his pain (relieved) by talking about the problem , about the grief.

I saw he understand why he was sad, and I let him keep talking about it; because sadness can be cured by talking about it.