An Observation
Miriam loved science. It didn't ask anything of her. The rewards were in unravelling the puzzles to find the solutions. She didn't have to be civil with science, she just had to be patient and observe. And she was excellent at observing.
Therefore, it didn't take long to notice the change in Matthew. He was still focused and dedicated to find out why creatures were becoming extinct. However once he had met Diana Bishop, there were changes. His determination to locate Ashmole 782 which he believed had the answers they were looking for, was still the same. At first he claimed his interest in the witch to be just trying to get hold of Ashmole 782. A book only Diana had seen recently. But then it became more.
It had been decades, to the best of Miriam's knowledge since Matthew had gone on a date, let alone with a warm blood. He was overprotective to the point where he sent Marcus to watch over Diana if he couldn't be there himself. And when Marcus convinced the witch to donate a blood sample, he would not allow Miriam to take the sample and insisted that no vampire but him would draw her blood. Now it was clear he was craving her. This would not end well and could have repercussions on the work they were doing at the lab.
The first sign that it could be more than just craving was when he decided to take Diana home to Sept-Tours to keep her safe. That was like walking into a lion's den with a juicy steak in your pocket. It was also the equivalent to taking a potential partner home to meet your Parents. Ysabeau de Claremont was notorious for her hatred of witches. Even if Matthew was her favourite son, this would not go down well. Diana would need all of her courage to make it through a stay at Ysabeau's home. How Miriam would have loved to have been a fly on the wall for that meeting.
After the lab had been broken into, it was practically like a neon sign. Miriam knew better than anyone what the signs were that a Vampire had mated. And there was no doubt that Matthew had found his mate even though she was from another species. No matter how much he denied it and tried to stay away from Diana, it was too late.
On the upside there was no way Diana Bishop could be as bad as Juliette. For someone created especially to attract Matthew, Juliette was incredibly clingy. Matthew had never been attracted to clingy women. It had been remarkable that their relationship lasted as long as it did and rumour was that Juliette was still pining for Matthew. Which would make her even less desirable to Matthew. The only emotion that would get her would be pity. And not even Juliette was desperate enough to settle for pity.
On the down side, Diana was a witch, which could be a whole lot of trouble or a blessing in disguise. Either way it was a forbidden union. But Diana didn't seem to have the same pre-conceived ideas about Vampires that most witches did. She even seemed to want to help find the answers they were looking for. Time would tell which way it would go. And how it would affect the rest of them who were merely observers.