Hilary Duff -- Stuck with $6,000/Month Bachelorette Pad ... As Reconciliation with Husband Looms

EXCLUSIVE

Hilary Duff might have just made a $6,000 per month mistake -- she recently signed a lease for a fancy bachelorette pad ... but now she might be getting back together with her estranged husband Mike Comrie.

Real estate sources tell TMZ, Duff signed the lease for the 1,500 sq. ft. 2-bedroom house a couple months ago -- soon after she and Mike announced they were separating -- but you may have noticed ... the "separated" couple hasn't been so "separated" recently.

Hilary and Mike have been hanging out a LOT -- Hilary even addressed the ambiguous situation, saying, "We love each other so much, and we love spending time together ... We don't know what our future looks like right now."

So it's unclear if Hilary plans to live in her new house ... or if she plans to let it sit Hilary-less, while she continues to live with Mike in their $3.9 million Beverly Hills mansion.

Sources close to Hilary insist her sister Haylie Duff currently lives in the home -- even though it's in Hilary's name -- but our real estate sources tell us, Hilary has spent significant time there.