He's Saleens' father and he doesn't just trust anyone. In fact due to having his wife taken captive by the Marauders of the surface clans, he didn't re marry.

When Lothaire was the young Prince of the Crimson Scar Kingdom, he actually had trouble befriending any suitors. Until he bumped into a princess while flying around a scared lake that was above ground. While someone else was interested in the same princess and didn't like the fact that Lothaire was with her. Causing 2 vampires to duel it out until one of them was called back, exhausted, or somehow dead. The duel lasted about 3 hours. The other collapsed from exhaustion, leaving Lothaire the victor. The 2 later married after 15 years since they met up. 3 weeks after their first (and only) born (Saleen), Lothaire's wife was kidnapped from the castle. Making Lothaire to stay at another Kingdom (With relatives) for a few months (or a year). While the soldiers looked into a passage where the other clan broke in and how they can fence it off. After that Lothaire became a little paranoid..If not more paranoid.

He gave Thorin a chance because, Thorin did bring Topaz (His grand daughter) back to the Kingdom alive and healthy. Right now Lothaire just hangs about the Kingdom and occasionally visiting his child and grand kids (like most grandparents).