It turns out that Zoom was much closer to Barry and Team Flash than they could have guessed. Jay Garrick, or at least the man claiming to be Jay Garrick was Zoom all along. Speaking to Variety, Flash showrunner Andrew Kresiberg explained---
"Zoom’s identity has been revealed: He is HunterZolomon, a.k.a JayGarrick. How all of that plays out and what’s actually happening, we’ll leave for after the break, but we wanted to go out on this run of episodes with a big reveal, just the same way we did at the end of episode 9 in season 1, where we revealed that Harrison Wells was the man in the yellow suit. Zoom’s identity is finally revealed. For us, it could only happen because of what happened last season. For Barry and the others, as much as they were stung by Wells/Thawne’s betrayal, he had been their mentor and friend and they all felt that vacuum when he was gone. Jay had been watching them and knew that so he was able to masterfully step into the role each of them needed. He became a friend and mentor to Barry. A love interest to the heartbroken Caitlin. He skillfully played them all."
If you're looking for more answers, you'll unfortunately have to wait a bit as The Flash is going on a mini hiatus until March 22. Speaking to E!, Kriesberg added ---
"We'll be learning the truth about Jay Garrick as the season progresses. Some of what he told Barry and the team was true and some of it was misleading. At the earliest stages of planning the season there was some discussion that Zoom was Barry's Earth-2 doppelganger but we very quickly moved away and fell in love with the idea that it was Jay."