I have to add something. I forgot that this "boyfriend" has a good relationship with his mom.
Well, if he decides to get married, he better put his new family as a priority, if he can't do that, then there's no marriage (same for the girlfriend).
I still think getting married is just between 2 people...I guess I don't understand the mentality of involving 2 families. Whatever choice your boyfriend's/husband's mother makes in life is her business. You can advise, but ultimately it's her life and she can do whatever she want, and your boyfriend should not be responsible for. (same thing as if your boyfriend/husband's dad is a murder/criminal, that doesn't make him one, he's not responsible his dad's doings. ) As long as the boyfriend is a good guy and loves you and if you love him, I don't see any reason of not getting married.
btw, I would think there are enough problems to deal with as a family when you get married, why would anyone want to involve parents or in-laws? When you are married, your priority should change to your spouse and kids, that's your nuclear family. Taking care parents/in-laws would be when you have extra time/effort/money and only if those actions don't hinder your current family relationships.
I guess I don't agree with the logic "you must take care your parents". Your responsibility should be your kids and your spouse. I would never expect my kid to take care of me, it would be nice bu I would want to be independent and not a burden to someone else. It's your choice to have a child, not the child's choice to be born. When you are ready to be a parent, you better be responsible for taking care of the child, but NOT Expecting something in return. That's not a reason to have a child. Don't have a kid if all you want is someone to take care of you when you are old. Save and invest your money and hire a care-taker if that's what you want.