Constant by Elizabeth Munro
As a Core Alliance soldier, Rye knows the grind of skirmishes on one forgotten planet after another. Then six years ago he discovered loss when the woman who meant everything died in his arms. Now, a chance meeting brings her back into his life. Under pressure to hide her from his superiors and rocked by the truths hidden in her past, Rye can only take one path. Follow his heart until every piece of it, and hers, heals.
Angel has secrets; why she joined Core and why she never sought Rye out when her body was stolen from cryo and put back together. She fights her own battle against the Aphids, at first for vengeance and now to protect the little piece of Rye she brought back from the other side. When she finds herself back in Core hands, she has no choice but to allow Rye to take her home and in doing so, she endangers far more than the quiet community which brought her back to life.