Warning: this is kind of big, but I felt like I should give some kind of explanation here

Read if you are interested, and sorry for any inaccuracies!
Well, it goes way back... the first instance of cooperation that I know of between the two countries was when in 1147, British crusaders stopped in Portugal along the way to the Holy Land, where they helped (paid help, obviously) our first king, D. Afonso Henriques, conquer the city of Lisbon (which is now our capital) from the Moors. However, the treaty itself only started in the 14th century, during the crisis of succession here. England provided military support to the would-be king (who married an english princess to seal the treaty btw), a bastard son of the last King. I believe this might be when the British first started to have a hand in wine commerce (Port wine) in the North of the country.
Ofc, there's no particular reason you would have learned about that above, since it only really matters to Portuguese. Internationally though, the alliance was important during the Napoleonic Wars, since Portugal was the only country that continued trade with England after the napoleonic blockade, loyal to their alliance. Subsequently, Napoleon had Portugal invaded, and England came to help. With the joint forces of Portugal and England, they managed to free Portugal and then Spain. In the meanwhile, our royal family fled to Brazil, to get away from the war (which was pretty bloody I assure you) and enjoy some holidays.
Of course that the British benefited a lot with this one... they mantained a presence in Portugal, to the point that it could be considered that the UK was governing us, for approximetly 13 years. Beresford was the head of it all, IIRC, putting english officials in political places. Portugal lost it's colonial commerce exclusivity, and numerous of portuguese soldiers had to fight in some of the UK's wars. We managed to pull out of it with a Liberal Revolution in 1820, which marked the return of our royal family and the expelling of the British, aswell as the start of a liberal monarchy.
The British helped again during the Portuguese Civil War in the 19th century, by siding with our Liberal Party, led by D. Pedro II (the king that fred Brazil btw). And then during the spliting of Africa by the european countries, the British presented an ultimatum to Portugal, demanding that it disoccupied the territories from Angola to Mozambique, since they wanted to build a railway from Cape Town to Cairo. That was harsh... and contributed to the fall of our monarchy, that we surrendered to the UK terms.
Then again, internationally, we Portuguese entered the WWI at the request of the UK, sending a lot of troops to Central Europe, Flandres, iirc (which btw, were left there with little support, around 10 000 died). It had heavy economic and political consequences, and contributed to the fall of the democracy and the institution of a militar dictatorship. Then, in WWII, we managed to stay out of the war, and our dictator convinced Franco from Spain to do the same. However, we provided military bases to the Allies in our Atlantic islands.
That is pretty much all that I can remember about it. I can see why it isn't much of a big deal to anyone that is not portuguese, even the british

No, we don't. We mainly learned about WW1 and WW2, life in the middle ages, the industrial revolution and the rise and fall of the British Empire, with some ancient history like Rome and stuff thrown in there occasionally. I think Portugal is only mentioned in football to be honest.
This does not surprise me in the least, unfortunately

ps: Sorry for the big post!