Thank you for waiting. There are fewer experts on European Law than in other categories.
The answer to your question is yes, in principle. The principle enshrined in law is that the co-signed of the mortgage becomes the co-debtor of the creditor. When the main debtor cannot pay, then the creditor is entitled to go after the co-debtor.
There are variations on this, however, depending on the terms of your contract. Normally, the co-debtor has the right to ask the creditor to go after the main debtor first. This right might have been waived under the contract, but it is best to check. If the right has not been waived, then the creditor must enforce against the main debtor, including against the mortgaged property itself, before coming after you for the rest. This is something creditors do not like, because sometimes it is quite complicated to enforce against the main debtor (for example, if he is bankrupt already), or to organize the sale of the mortgaged property. Enforcing this right happens through the courts, i.e., through an action, entered by you before the local court in Portugal where the enforcement is taking place, against the enforcement, for being against the legal order of priority of debtors.
Supposing this right was waived, or the creditor has already taken as much as possible from the main debtor, and still has money to recover, then he may come after you. However, there are, again, some stops in what he may do. The main rule is that he cannot come after your immovable (house, land) unless and until he has enforced against money and other assets (he may enforce directly against an immovable only if the respective immovable was included as a mortgaged asset in the contract). Furthermore, you have the option to propose (again, if he does not agree, then through the local court) a payment schedule, a trade-off for some property or any other idea that you may have to pay him back. But, if there is no agreement, he may put a charge on your salary, bank accounts, and failing recovery of the full amount, actually start selling assets that you own.
I hope your case does not reach this point, and that either of the bars will apply (i.e. that he must go first after the main debtor), or that you will reach a settlement with the creditor. If you are planning on taking up legal action against his enforcement procedure, it is best to appoint a local attorney, who knows the practice and the administrative requirements of the local court. If you need, and send me the name of the city, I can send you a list of English-speaking attorneys in the region of interest.
I look forward to any further issues and to your rating.
Dr I L Vlad