Duties of spouse separated with wife

Asa, My husband and I are separated after 30 yrs of marriage, we have 4 children, 3 of whom are adults but not married. Although we are separated living in separate houses, we continue to have intimate relations, and therefore he spends one night a week in the family home. He is considering taking a second wife, which I have no issues with. What I would like to know is, what are his financial responsibilities towards myself and the children? Currently he is paying the bills, but has stopped paying the mortgage/rent, he pays for the Asian groceries, which is less than £100 a month. This is all he is paying. I work part time, and therefore can afford to pay for my own clothes and essentials. The house he currently lives in is also ours, and there is no longer a mortgage. He lives there with his brothers and I am sure they are paying the bills there. His job is that of a private hire driver. He is saying that when he takes on a second wife, he will be unable to run 2 houses, and therefore wants me to pay the mortgage. My older children pay for some money towards the food shopping.
I feel this is unfair, as he eats here, has relations with me, and the only thing is he spends the night at the other house. (we have irreconciable differences). We have come to this arrangement due to having one teenage son, and do not want to disrupt the stability. He says he does not want to divorce me, and this arrangement suits me well. Please can you let me know what the Islamic rulings are in a situation like this.
Jazakallahu Khayr
S

Wasalam

May Allah bless you.
In general, if the children are at the age where they can work and earn their own money, then the father is not responsible to support them financially. If they are physically unable to work and have no income, then he still has to support them.

However, he is responsible to support you financially. This includes paying for the cost of food, clothing, house and the cost associated to it such as energy bills etc.
You should speak to him and let know how you feel and you both should try come to an arrangement that suit everybody.

And Allah knows best!