If there is a large wage gap, some couples go by percentage of income to make things more fair. I am going to use round numbers to make it easy:

DH makes 100K

You Make 50K

DH make 2/3 of the household budget you make 1/3- therefore you pay 1/3 of everything. 

** Side note- if you son is an adult (not in college)- it isn't your job to save for him. That is his job and it shouldn't be considered in you budget for your household**

Is his 14 year old living with you? If so, I'd think he should be paying 2/3 of the expenses, rather than 50%. I also think a loving, committed partner who earned significantly more than the other partner would want to pay a share commensurate with his larger income.

There is no hard and fast rule.. but I do think the adults in the home should contribute proportionally in some way.. whether it be weighted on income.. or ocupants of the home(and relative time living in the home).

Other factors can come into play too.  For example.. if this is your home originally.. then there may be more argument that you would split things with some thougth to the fact that you own.. while he may be "renting".

If you.. the lower earner moved into his existing home.. it is somewhat unfair to expect you to pay a rate that would exceed what you might ordinarily find to spend on yourself if you were living on your own too... think huge disparity in income.. he wants to live in the gated golf course home.. you would be fine with a modest townhome in a more suburban neighborhood.. it's not fair for him to expect you to pay 1/2 of something you wouldn't want and probably don't need or enjoy as much as he does.

But, also keep in mind if you expect to keep a room for your child open for them.. and if his kid is Pt

.... you are both technically using similar portions of the home.  I would think that he would want for you to both feel that you are treated fairly.  The best thing is to talk to him.. tell him yourconcerns.

If he is a good/supportive partner.. he will find a way to make things work in a way that allows you both to reach financial goals.

We keep our finances as separate as possible. There will always be something that comes up - for example DH believes in providing a car to his kids and I disagree. He knows I am not supportive of his buying his college age daughter a car this summer for a 6 week internship (if it is not cancelled), but ultimately it is his money, and as long as he is paying his half of the household expenses and maximizing his retirement savings, it's not my place to say. Same goes if I choose to help my daughter with Medical school and he disagrees with any education support beyond Undergraduate. This works because our incomes are fairly comparable (I earn more but he still does well) and each of us can stand on our own including the CS he pays (I barely receive any CS).

Nevertheless, I expect one day there to be a need to determine which kids receives support for something. We all hope that our kids will grow up to be totally independent, and of his 4, 2 are fully launched, 1 on track to being very independent and his youngest...let's say he will never live in my basement! My 3 are tracking well so far. Even if a kid is totally on point, life can bring challenges and even tragedies and sometimes parents help out (and kids help parents...I would help my in-laws - love them). I hope this is never an issue. I know that I would have a very difficult time allowing any resource to be moved from me or my kids to his kids. Not to DH himself obviously, but I really don't know his kids or have any relationship with them. I would not ever want them to benefit from my hard work. We set up trusts to hold all assets in the desired proportions including deed to our home (80% mine as the proceeds from the sale of my 'single Mom house' went into our home) - I want to be sure that skids who had a dippy useless stay at home mother, get nothing from me, ever including through inheritance. 

So unless you are ok with a reallocation of resources to skids, do whatever you can to protect yourself!

Pay 1/3 for everything. You're 1/3 of the family. Skid is not yours. You are not obliged to pay for her. Do not pay for their groceries either. DH needs to grow up.