Close aides dismissed speculation that the Foreign Secretary wanted to take a job at the European Commission after a troubled year in which he left his wife and married his mistress, Gaynor Regan.
But a close friend conceded that Mr Cook, 52, had thought about resigning several times since his affair with Ms Regan became public last summer.
"It has been rocky at times," the friend said. Aides are also concerned about the publication of his former wife's book in January.
Margaret Cook's revelations about Mr Cook's infidelities and their marriage breakdown are expected to be explosive, and damaging to the Foreign Secretary. However, Mr Cook was clearly supported by his party yesterday as he argued for a more positive role for Britain in Europe.
With the SPD victory in Germany last Sunday, and with 10 of the 15 EU member states now having centre-left governments, he said European politics were entering a "new era".
"We want the single currency to be a success ... too many jobs in Britain depend on exports to Europe for it to fail.
"When the time is right, we will make our decision on whether to join on the basis of a hard-headed assessment of whether it will be good for the economy in Britain and good for jobs in Britain."
The Foreign Secretary added that expansion of the European Union to cover Cyprus and the new democracies in Eastern Europe was in the interests of Britain's security - "not just because it is in their interest to share our prosperity, but because it is in the interest of our own security that they share our stability," he stressed.
Mr Cook pledged that Britain now had once again got respect around the world.
"Respect, because the values and freedoms we want for ourselves, are the same values and freedoms we demand for others," he said.
"Respect for our new influence in Europe.
"Respect because we stand firm with the United Nations against those tyrants who challenge its authority."Reuse content