Grimlock ♥ Ultra Magnus

This is a great series exploring time travel, loss, and war.   Alexander Dorian, one of the Vine - the aliens who worship the X-O Manowar armor - has decided he likes Earth enough to save it.   To do this, he has to betray his people, and join with both Aric - who wears the Shanhara armor, and has a growing bond with it. 

Enter Ninjak.   Talented, merciless and relentless, he is whom the Vine send after the Shanhara armor, and Aric.   Unless Alexander and Aric end up killing off one another first.   After all, Alexander is presumed dead by the Vine, as Aric killed the special forces group sent with Alexander after the armor. 

And as the insults mount - a human bearing their sacred armor, that armor being used against the Vine, and to kill some of them, the secret of their changelings in danger of being revealed - they decide it best to destroy Earth and all of humanity by sending in an invading fleet. 

Once again, it's a breakneck pace, although all the background is in the first volume.   This is definitely not a stand alone.   Human/alien-armor bonding?   I am all over that.   I highly suggest this series, in fact.