The UK Royal Family didn't think too highly of Wilhelm, even before the war. He was regarded as obnoxious by them. He was also disliked by the Russian royal family, his other cousins (he had a lot of royal cousins, these weren't the only 2 countries). Despite this he often went to England, as his grandmother Queen Victoria treated him courteously and he seemed to crave her attention.

After the war he moved (some would say fled) to the Netherlands, which had remained neutral. If he was reviled before the war, he was hated after the war, with King George V calling him the "Greatest Criminal in History". The treaty of Versailles, article 227 expressly provided for the prosecution of Wilhelm "for a supreme offence against international morality and the sanctity of treaties". The Netherlands refused to extradite him. He would spend the rest of his life there.

Wilhelm spent the rest of his life hunting, chopping wood (which he loved to do for some reason), and studying archaeology. He mainly resided in the Netherlands, but also purchased a house in neutral Greece and spent time there with his archaeology passion. He entertained guests and kept up with European politics. At first he hoped that Hitler would restore him to the monarchy, but eventually grew wary and suspicious Hitler. However, after Germany's early successes in the beginning of the war he began to enthusiastically support him, while at the same time reminding Hitler that he (Wilhelm) could still be King, saying things like "My Fuhrer, I congratulate you and hope that under your marvelous leadership the German monarchy will be restored completely.". Hitler, for his part, thought Wilhelm an idiot, and could never forgive him for losing WW1 (which Hitler served in).

When the Netherlands fell to Germany in 1940, Winston Churchill offered Wilhelm asylum in England, an offer which Wilhelm refused. Interestingly, I doubt that this offer could have been extended without the British royal family's permission.

Wilhelm died in 1941, just weeks before Germany's disastrous invasion of Russia. During the last year of his life he hated England, calling it the land of the anti-christ and accusing it of being ruled by Jewish Freemasons. Oh yes, he was an anti-Semite much like Hitler, saying things like "The Jews [are] being thrust out of their nefarious positions in all countries, whom they have driven to hostility for centuries." and "British people must be liberated from Antichrist Juda. We must drive Juda out of England just as he has been chased out of the Continent."

So in conclusion, Wilhelm was not well liked by his British cousins before WW1, and after Queen Victoria's death in 1901 he lost the only person in the UK that tolerated him. After WW1 he was reviled, although King George V did stop short of calling for his execution post ww1.