Loudwire says,

The song starts with a few somber sounding opening notes before building in intensity toward some crushing bass and guitar work. Welch is flanked by Breaking Benjamin’s Jasen Rauch, who produced the song, JR Bareis (from Islander and Love and Death) and Dan Johnson from RED. Head shares vocal duties on the track with Bareis on the track, which can be heard in the player above.
Head tells us, “‘Lo Lamento’ is a song that came from an idea producer Jasen Rauch and writer Mark Holeman had on our last album, Between Here and Lost. It was actually the original chorus for our song ‘I W8 4 U,’ but it sounded way too melodic for that crushing song as you can imagine. To me ‘Lo Lamento’ paints a picture lyrically about infidelity and a once picture perfect relationship left in ruins.”