Was it written by a native speaker of Japanese? It seems somewhat awkward or unnatural to me. Maybe I need more context to understand what the writer wanted to say. Anyway, 慰みもの means a plaything. It can literally be something to amuse yourself, or it can figuratively be someone to be made fun of or to be used for other's amusement. In the latter sense, it often implies sexual relationship. I hope this helps.

Acturally, I am a little bit confused now. Still, thank you for your answer. I appreciate it.

This is fanny First is ok" If you go your home land" Next one is never say in normal sentence more ever in love letter Nagusamimono (In Japanese actually look down a people should say "Nagusamimono ni naranai Youni comes negative tence coming is nornal " (mean not make fun from others" might be but good way to guess can if the person in non japanese ( might be a funny person) even if so little funny also akirameru is give up mean so that do not write me letter if the person If I write as friend or more good relationship ”慰みものにならないように、手紙をあらためるべきだ　（Naguakimono ni naraNAI tameni tegami wo aKIratameu bekiba) is make sence Just few word mistake will be charge mean totaly so you should careful when you make a sentence.