If Nick continued to love Kelly as his despite knowing the truth, the situation would be no different than what's playing on screen, Kelly's life would still be in danger because of him.
And if Kelly turned out to be a "bad seed" type of wesen, having watched Nick during the El Cuegle episode, Nick can't act any different. He'll still see Kelly as his son and try and shield him as best as he could. Nick acts on the facts presented to him in the now, not what may or may not happen. It wouldn't matter to Adalind one way or another, because Kelly is her baby and she’d protect him with her life. Could Nick and Adalind find themselves on opposite sides regarding Kelly's fate? It's still too early to tell. He just found out Diana committed murder, twice and it didn’t even register and Diana's not even his daughter.
And if Kelly turned out to be a "bad seed" type of wesen, having watched Nick during the El Cuegle episode, Nick can't act any different. He'll still see Kelly as his son and try and shield him as best as he could. Nick acts on the facts presented to him in the now, not what may or may not happen. It wouldn't matter to Adalind one way or another, because Kelly is her baby and she’d protect him with her life. Could Nick and Adalind find themselves on opposite sides regarding Kelly's fate? It's still too early to tell. He just found out Diana committed murder, twice and it didn’t even register and Diana's not even his daughter.