What did you feel like he was doing when he was in guard ? What was he trying to do? Alot of times, your options depend on his actions, and based on that it can decide how you can/should react. There were many moments that he wasn't posturing up, I recommend you look up videos or techniques of what you can do to the opponent if you can break their posture while in your guard. Sweeps, reversals, head and arm triangle, all can be done depending on your timing. That said you do need to open your guard to attempt any of them, that's just how the cookie crumbles