Married to UK citizen

I am married to a citizen of the UK. We have been married for about a year and a half. We got married in North Carolina, and we both live here now. She has her provisional green card that is good for two years. We need to reapply in a few months for the new card. So, my questions:
Living apart is not an option, she quit her job and has no income. I cannot afford to pay for a house and an apt at the same time. How do we do this.
Second, at what point should i let immigration know that we are seperated and will not stay married.

That is more of an immigration question. You can negotiate a separation agreement while you live together, but the clock for divorce doesn’t start until you live apart.