Short answer. Your spouse does, out of exclusive property. Where a donation is onerous and the partnership advanced the charges, the amount is borne by the donee-spouse's exclusive property. The partnership paid it in the meantime, but the burden is accounted back to the spouse who got the gift.
What the law says
If the donations are onerous, the amount of the charges shall be borne by the exclusive property of the donee spouse, whenever they have been advanced by the conjugal partnership of gains.
Family Code, Article 114 — Charges on Onerous Donations. Read the full provision →
What makes a donation onerous
A simple donation gives without asking anything back. An onerous one imposes a burden on the donee — a mortgage or debt that comes with the land, an obligation to support the donor, a sum to be paid to a third person. The burden is the price of the gift, and the article's logic follows from that: the spouse who received the benefit should carry the price. Whether a particular donation is onerous is a question of what the deed says, not of how the family felt about it, and it is the first thing to establish because the whole rule turns on it.
Advanced, not assumed
The operative word is advanced. Nothing stops the partnership from paying the charge as it falls due; households pay what needs paying out of the money to hand. What the article denies is that the payment ends there. The amount is borne by the exclusive property of the donee spouse, so the partnership has effectively lent the money and is entitled to be made whole. This is not a claim the paying spouse has to prove was made under protest, and it does not depend on anyone having objected at the time.
The reckoning comes at liquidation
In practice nobody settles this while the marriage is running smoothly, and the article does not require them to. It becomes a live number when the partnership is liquidated, which is when the accounts between the spouses are drawn and each side's advances and reimbursements are set against the other. The consequence of leaving it that long is evidentiary rather than legal: the entitlement survives, but the proof of what was paid and from where may not. A spouse who never separated the accounts will find the burden of showing the payments came from partnership funds sitting with them.
Keep the deed and the payment record together
Two documents decide this. The deed of donation, read for the charge it imposes — its amount, its terms and whether it was truly a condition of the gift rather than an unrelated obligation. And the payment history: the receipts, the account statements, the loan records showing which funds discharged the charge and on what dates. Where the property has since been sold or improved, the figures get harder to disentangle, so it is worth assembling the record while the payments are recent rather than reconstructing it at liquidation.