As a werewolf meeting your mate can be overwhelming. When Jason meets his they were both still children but in fear of losing her he bit her anyway. Before he could tell her the significance they are forced apart and he is commanded by his alpha (dad) not to see her or tell her. A command he had no choice but obey.
Now she has returned and the competing pack has set a time limit on when he can claim his mate or it is open season. But he is still not allowed to tell her that she is his mate.