A friend of mine shares his iPhone with his kid through iPad. So all the messages I sent to him could be read by his kid. I'm concerned?

I brought this issue up to him hoping to find ways to solve this issue. Because I feel really uncomfortable that my messages to him is open to his family members. He would not do anything about it, saying convenience to his family out weigh my concern.

Is he completely ignorant of my concern or what I'm asking is too much?

What you are asking is too much. Keep all messages superficial and save anything a kid should not read for private conversation. I can't sext my spouse because our kids sometimes pick up my phone but that doesn't mean we never say things to each other. Life with kids is just this way.

Just don't send hirn rnessages if you don't want his kid to read thern

He is a bit of a d! Ck if he doesn't understand your expectation of confidentiality. Don't send him messages. Easy.

So don't post anything that they couldn't read. If he can't respect a certain level of privacy between you two then maybe its time to say goodbye?