https://hetalia.fandom.com/wiki/Poland/Lithuania:
Poland/Lithuania is an extremely common pairing involving the characters Poland and Lithuania. It is also known as PolLiet or LietPol. [...]
It is thought by fans that Poland does care for Lithuania, yet is simply too stubborn to show it, preferring that Lithuania adjust to his rules rather than let him do as he wanted. In more recent strips, Poland is far less selfish than he used to be. His apparent nonchalant attitude about Lithuania being taken from him has also been interpreted as him trying to laugh off the unfortunate situation (and his own impending first partition).
The dream sequence in Chapter 5 has been interpreted as being about Poland's true feelings for Lithuania, although it could also be that Lithuania simply believes deep down that Poland actually cares for him that way (even with his frustration towards how he was treated).
Lithuania's scars are another subject of debate among fans, with most believing that Russia inflicted them himself when he bullied Lithuania. Poland's discovery of the scars tends to be seen as the moment that he "matured" in their relationship, after the two were reunited.
Other fans believe that their relationship is a lot more strained beneath the surface than it would seem, due to the Vilnius conflict.
https://static.wikia.nocookie.net/he...20190906013751
Poland (left) and Lithuania (right).