OP, it sounds like you’re seriously catastrophising here. Don’t get me wrong, I’d also be angry if my DH made a big financial decision like this without telling me and me agreeing to it, but sit down and think for a moment about what’s actually happened here. It sounds like your DH’s friend has bought a new property before the sale of his old one went through, so he needed a bridging loan, and your DH has guaranteed the bridging loan, is that right? If so then this is not the same as guaranteeing the mortgage on his new property as it’s a much shorter term commitment.
Now presumably this bridging loan involves the friend paying the interest, with the capital to be paid off when the old house is sold? And there will probably be a long stop date, usually a year or so with a bridging loan. Is the friend unlikely to be able to pay the interest payments? If he defaults, then your DH would have to pay them, does he have a large enough income to do that?
The only scenario in which your house could possibly be at risk is if the friend’s old house doesn’t sell for an exceptionally long time and the long stop date passes. Even then, the bank doesn’t go from the repayment date passing to forcing a sale of your house in the space of a week. The friend would have time to try and refinance.
As I say above, you have every right to be angry, but in reality it feels unlikely to me in this situation that you are at risk of being made homeless.