Topic: Moving On-Site

I've been given a soft offer for an onsite position. In the past when asked who would occupy the unit with me, I'd always tell the hiring manager it would only be myself (truth). Afterward, I've always been offered the job in its entirety. Lately, when I let the hiring manager know my fiancee would be residing with me, I wouldn't get a callback. So my question is this: Do companies prefer their onsite managers to live alone? Is it a problem to have another living with you?