Don't just assume a person wants to marry you or will marry you because they are nice to you. A person can be nice to you but have no interest in you.
Don't just conclude he/she is interested in you because they asked about your family background, age etc...You have to be sensible enough; ask questions especially if you are in a relationship with them. If you are in a relationship with them and you still don't know where that relationship is heading to, then I wonder when! I understand you don't want to ask them so you won't sound desperate; Are you not desperate? Don't you wish to spend your entire life with them?
It is better to know your stand in any relationship than waste your entire years only for them to throw you off and invite you for their introduction. Be a detective for once; ask them where the relationship is heading to; No where, or somewhere?
Every relationship must not end in marriage I know, but I don't want to be in that shoe. If it's not heading no where, then keep it on the friend Zone.(Hello,Hi,How was your day? Ok bye)