Resonance by Lindsey Fairleigh, Lindsey Sparks

A week has passed since the confrontation with Set. Lex and Marcus have been biding their time in Florence, waiting for Set to make a move.
Just as they're settling in to their new life together, an act of vandalism on one of Marcus's most prized possessions reveals that their past-and future-is far more complex than they realized.
The past clashes with the present in this paranormal tale of ancient prophecies and warring gods. If you like Egyptian mythology, steamy romance, time-bending mysteries, and complex characters, then you'll love this sprawling time travel adventure.
MORE BOOKS IN THE ECHO WORLD
ECHO TRILOGY
Echo in Time
Resonance (an Echo Trilogy novella)
Time Anomaly
Dissonance (an Echo Trilogy novella)
Ricochet Through Time
KAT DUBOIS CHRONICLES
Ink Witch
Outcast
Underground
Soul Eater
Judgement
Afterlife