to assume his guarantor status for his ex would no longer stand?

[BathBubblesOfHell]

When DP got divorced he agreed to be a home owner guarantor for his ex so she could rent somewhere (she never worked). Since then, 5 years have gone by, he has sold that particular house, didn't own a house for a while and then bought another house with me - we are joint owners of it. I used to panic that if she didn't pay her rent we'd have to pay it for her but since time has gone on and the original house ownership no longer exists and his current house is xo-owned - Aibu / naive to assume that his guarantor status would no longer be enforceable should she stop paying her rent?

As others have said, only the terms of that particular guarantee document and her tenancy agreement will tell you the definitive answer.

I am not entirely clear from your OP on the setup- you talk about him selling " that particular house" but not clear which house you mean.

Is the situation as follows?

1. Ex rented house A 5 years ago.
2. Ex needed someone who was a home owner to guarantee her rent of house A.
3. Your DH owned house B at the time he signed the guarantee of the rent for house A.
4. Your DH later sold house B.
5. Ex still lives in house A.
6. DH now jointly owns house C with you.

Once again, only the paperwork specific to this particular arrangement will give the answer.

However, as a general observation, it is highly unlikely that your DH's guarantee of the rent of house A would be contingent upon him owning house B. All the landlord would have specified was that the guarantor be "a home owner" at the time of signing the guarantee, the reason being that he wanted someone with a decent credit record/ some assets.

However the guarantee documentation would not state that it was automatically enforceable against house B. So if he had been called upon to pay her rent he could have paid from liquid assets. Only as a very last resort would the landlord have sought to force a sale of the house to satisfy the debt.

During the period that your DH was not a homeowner the landlord's risk of not being able to get any money out of him was increased. However the sale of house B would not in itself have invalidated the guarantee ( though the guarantee might have coincidentally lapsed for other reasons).

Now that half of house C forms part of your DH's assets then in theory the guarantee, if still operative, could be enforced against his half of your house, but forcing a sale would be pretty tricky given the need to protect your rights.

As others have said, unless he signed a new guarantee when she renewed her tenancy, the guarantee has probably lapsed. It would have been the landlord's lookout to insist on a new guarantee with the renewal. But you have to see the terms of the original tenancy and guarantee to be sure.

Do let us know what the actual paperwork says.

He should have been given a copy of what he signed, which these days should be in clear English, so you/he should be able to establish hus liability without involving a solicitor.