should i tell my bf??

i’m 16 and I have been dating a guy for almost 4 months now. he knows everything abt me except the fact that i have some mental health problems. i don’t want to tell him bc i don’t want him to think i’m looking for attention or whatever. but the thing is when i have bad days and when i have depressed days i completely shut off and stop talking and i don’t know how to deal with it anymore bc he thinks i’m mad at him on those days and i hate that i’m making him sad. also sometimes little things he does like letting his ex copy his homework or something like that completely send my mind into a spiral that he’s cheating on me and secretly loves her and i just hate that i can’t talk to him abt it.