No attorney can realistically advise you online about the meaning and consequences of signing a document (letter of indemification) without having read it.
I assume your "roommate" who filed for bankruptcy was a co-owner of the house?
The information presented here is general in nature and is not intended, nor should be construed, as legal advice. This posting does not create any attorney-client relationship with the author (who is only admitted to practice law in the State of California). For specific advice about your particular situation, consult your own attorney.
I agree with Frank that more information is needed than can be discussed online. My recommendation would be to have a lawyer review the entire document and the surrounding circumstances regarding the house before you sign any documents.