What things are you doing that he is objecting to?
Are you spending only your money on the kids, or are your finances combined?
How long have you been together?
Well I have to say............I agree with you 110%
As a parent your job to be there for your kids do not end once they are grown............while it would be nice, that is a fantasy! And one I don't think many mothers would really want at the end of the day. What you have described sounds fair, and not anything that is to much. In fact, its pretty common for parents to get straddled with a lot more with their young adult children. It sounds like your kids need help every once in a while, and as a parent you are helping them. I see nothing wrong with this, as this is common place.
What this boils down to though isn't what "I" think......in the end it sounds like he was raised one way, and thinks all children should be raised that way as well. In the end it isn't who you are, and changing for him is just not acceptable.
Your children are the other part of your life, and he should respect that. Now if your helping them was causing serious problems in your own life (IE, money, time, work etc) then he would have a right to talk to you about it and tell you why he is concerned, but in this situation this is something he needs to learn to respect.
With that being said, you have a couple of options here. The first to to sit down and let him know how you feel about this. Explain to him that his behavior in this aspect is upsetting you and it needs to stop. If this is a breaking point for you then you need to be honest with him about it. Explain to him that if he can not respect this part of your life then you will have to consider your options. In the end if this is a breaking point for you then it is better to address this now then to wait until things explode.
If its not a breaking point then sit down and talk to him, let him know that while you appreciate his concern, this is a part of your life that you need him to respect and if he can not then it is something you will have to agree to disagree about. When you need to do things for your children this should be done on your own, without his involvement. Should he choose to express views, calmly explain to him that while you appreciate his concern, this is a matter between your children and yourself and your views are different then his. While this could upset him, the reality is if he does not like it then his option is to not involve himself in it.
Adult children can be a bone of contention in any marriage, but sometimes as a parent you have to take a step back and do what you feel is right in the end.