Bite of Betrayal by Damon Kinney

An 1100-year-old vampire and his 22-year-old human fianceé find their lives in danger when word of her pregnancy finds its way to a master assassin dedicated to making sure such babies never take their first breath.
Sagan: A new love, a new engagement, and a new life growing inside of me. I have big decisions to make regarding my own life and my baby’s if I’m going to be part of Terrance’s life forever. He’s devastatingly handsome, absurdly wealthy, charming AF, and well-endowed. What’s not to love? But when his long past rears its ugly head, I quickly find my life upended to a degree I would never have imagined.
Terrance: Finding one soulmate in a lifetime is fortunate, but I screwed that up more than a millennium ago. Then I find myself blessed to find a second, this one even more beautiful and precious, and I plan to claim Sagan as mine as soon as possible. But first I’ll have to fight off an ancient sect with a grisly objective that could destroy everything and deprive me of my joy.