"I wrote a small letter to Chern. and got a reply the next day. Please thank him and pass on our big regards to him."
"Do you have any news about Mal. and Nik. Dmit.?"
"How come up to now you've not seen [each other?]? And is little Chern[ychev?]. here? Give him my warmest regards if you see him. I wrote on the holiday."
All these quotes (and some others I've read only in Russian) from letters to Ritka applys to the same person - not Chernychev, but Malenkyi Chernogorets (little Montenegrian), Dzhurkovich, warrant officer of the Ljubljana's regiment, who was seriously wounded in 1916 and became one of Olga's favourite patients (she wrote in her diary: "He is very nice, and I love him").
Tatiana signed his name on this photo:
I'm not sure about the order, but I think it's him: