you have to realize that those against marriage are unmarried themselves therefore no need to ask their advice. wait until happily married couple give you their opinion on it - vashti, giga and whomever else.
in my opinion he is very shallow to ever think about how much it would cost him to divorce you considering that he has 2 kids with you. it would've been an argument if no children were involved. first of all your children are bastards until he marries you. he gets to introduce you as his wife, instead of baby mama or girlfriend. security of your children in case something happens, such as divorce or death. your peace of mind should be considered as well, the happier you are, the better you will treat him, and not resent as you do now.
second of all, your children will be brought up knowing the right values in life. comparing to having your daughter being impregnated and not being married, cuz my momma did so. or having a son who does the same to other females and learning how to respect women early in life.