Years at War Series by eristarisis
Part 1: Triwizard Warfare
https://www.fanfiction.net/s/6859194/1/Years-at-War-Part-1-Triwizard-Warfare
Het Harry/Hermione, Harry/Fleur

Excellent1st of three in the series. There is action galore and beginning in the 2nd story sex. The characters are well fleshed out and behavior fits the world they belong in. That said they are also the most depressingly sad stories I have willingly read. I usually try to stay away from unless I am sure they have a happy ending. This one has a strange optimistic ending. It is a true depiction of war, good guys lose as often as they win, poor Harry never catches a break. That said this author is very, very good and makes no bones about writing a story where everyone dies. Well not everyone but close. It is a story about child soldiers doing the work that the adults failed at. About loss, betrayal, that forgiving an enemy can lead to a knife in your back and how sometimes love is just not enough. Good intentions can lead to bad consequences and sometimes your temper can be your own downfall. while they may not be my favorite type of story, they are some of the best I have read.

 Part 2: Years at War: Legion Born
https://www.fanfiction.net/s/7068631/1/Years-at-War-Part-2-The-Legion-Born

Part 3:  Years at War: Wizards War
https://www.fanfiction.net/s/11158834/1/Years-at-War-Part-3-Wizard-s-War