You stated in your very first post that it was unliveable (your word) from day one, you also mentioned the following, no tiling, no appliances, vines and rubble, broken pipe, house done up in a haphazard manner, holes everywhere.
You then put up with heating constantly breaking down mid winter, you should have left then.
After the first instant with the intruder, in your house, you did not change the locks yourself, I don't care about the landlord, I would have done it myself immediately for sure if I had met a stranger in my house, even after meeting the said person again you didn't do anything and then you mention you're from the country. I think you guys are extremely lucky and you should thank your lucky stars that the incident turned out so trivial, there are people in the Irish contryside tied up and left for dead. Whatever about the landlord responsibilites, you yourself did not take the action required to secure your safety so to me you didn't think it was important enough.
As a previous student and a landlord who will not let to students, it seems to me you took the house because you were in a hurry/desperate/preoccupied with college and other more serious matters. Now it's the end of the year and short of cash you want to cash in. Then it's simple don't pay the last month's rent and do a runner like countless others before you. Do you think your landlord isn't expecting it? He's factored it into the rent he charged you. And a landlord that lets a house like that knows exactly what he's at.
Next year when you're more mature, rent a proper house and don't be rushed into anything. Your experience is only part of growing up. You never know you might be the landlord in the future. No pun intended.