While keeping her secret to herself is perfectly in character, we also think it's a bad idea. We get it. Spencer wants to believe there's more to the story, and she wants to find out the whole truth by herself. But by doing so, she's putting her friends in danger.
Spencer isn't the only one who trusts Toby. Emily (Shay Mitchell) is his friend, and the other Liars think he's a good guy. By leaving them ignorant, she's opening the door for Toby to continue to take advantage of the other Liars' faith in him. He could get information from them — or worse, lead them into danger.
That's not even touching on the number of ways the "A" team could use this secret to manipulate or hurt Spencer herself!
That's just our opinion, though. What do you think: Should Spencer tell her friends, or is it alright for her to figure this one out on her own?