Ok, I could really need some help with this one. What should I have done?

It is pretty clear if you watch this match that you were playing non-optimally. You had those 2 cons sitting above your base totally idle for ages: They could have been making defenders to snipe his LLT, or an llt of their own to retreat to, or repairing your commander. You had 300 metal at any one time, he had comm income only, and wasn't producing from his factory.

You realized (perhaps too late) that you can actually outrun and outrange his comm. In fact, when he killed you, that was his last bullet before you were outranging him. So with better micro, you could beat him with comm alone.

You should engage with your glaives when he is fighting your com, not independently. The HE-EMG is too good at anti-swarm, and you do more damage this way.

He had an auto-repair module, so you should have tried to hit him with everything at once rather than wear him down. You werent going to win by running away and making more mexes, (he would just regen and com rambo you), if you needed metal (you didnt) there is plenty of reclaim on this map to last long enough to beat him.

I honestly feel that pulling back the Glavies was a mistake, they should have stayed where they was and prevented any potential construction plane. The biggest mistake was the constructors taking a nap for most of the time.

Duh.. I think you can set your comm to repeat and Q-queue an LLT in front of it to block every single shot and shoot in between.

Stuff's been idle pretty much. Has already been said. I think you should've kept building LLTs while your lab was being shot at. 3 or 4 just as Jasper said.