How will my filing bankruptcy affect my wife if we are separated but not legally?

If you're living separately then you can file a single bankruptcy which will not involve your wife.

I'm not sure what you mean by "legally"? If you and your wife separated, and are living apart, she will not be part of your BK filing.

There is no reason why a married couple need to file jointly. You could file on your own, but you will have to disclose your wife's property.

If the property your wife owns is community property, even if titled in her name alone, any equity your wife has might well be vulnerable to being taken by a bankruptcy trustee to pay a portion of your debts.

It all depends on specific facts, maybe a lot, maybe not at all.

As in most such situations, the devil is in the details, things like "how is the property titled?" and "when did the separation start?" and "did you file a petition for dissolution?" There are no simple answers in bankruptcy and that is why it is imperative that you locate and retain a competent bankruptcy lawyer before you do anything respecting a bankruptcy filing. I know there are books and websites that tell you it is possible to file your own bankruptcy and save thousands in fees, but unless yours is the absolutely simplest, least complicated and straightforward situation, you're going to run into problems and need the help of a pro. Call your local bar association and get a couple of referrals, then speak with them and find the one that's right for you. I tell my clients that going through bankruptcy is like the Tim Robbins character in Shawshank Redemption crawling through the sewer pipe to get to freedom. Its long and its hard and during the process you'll think it is the worst, but when you're finished and receive your discharge, you're free to start your financial life over.