I watched up to 14mins and I can tell you what lost you the game:
1. UEF gun upgrade - this can 1-shot any Aeon T1 unit.
2. He had upgraded 3 mexes to T2 by this point.
However, I took lots of notes so I will put them into sentences and hopefully give you some constructive criticism.
Starting out, you sent an engineer east to get those two mexes. The travel distance is further than getting the two on the cliff, and it also delays the time it takes to get radar up on that cliff.
Too many initial engies, you made at least five before making anything with a gun. My rule of thumb is 3 engies then 1 LAB, but of course it can vary depending on the map.
Your ACU stayed in the base a bit too long, and when you did send it out it went north. Put it in the middle and stop the enemy getting a foothold there. Also from an area-denial point of view, middle of the map is nearly always best on a 5k map, especially that one.
First military units were scouts, often building one LAB first with no scout is a useful thing - send it to the mex point you estimate will have an engy by it when you arrive. Invert your own build plans to help you decide if it's a map you don't know well. Unaccompanied scout is suicide, it's not even capable of killing an engineer. The south scout was killed very easily.
However, the scout in the middle was good and spotted the enemy ACU, this is valuable intel. Well done on running away with the scout too.
I've got a note that says not to build LABs past the initial raids, but TBH I think you got that just about right after having watched on further.
Good sending tanks to east side.
Also good sending one LAB into enemy base, causing his entire army to chase after it. That let you raid in the west with a couple of LABs and take out a couple of mexes.
At 6:40, your reclaim was 447 mass, his was 2513. The difference is the cost of the two mexes he upgraded early on and helped him win the game.
At 8:00 you had no E-storage, meaning no overcharging. I often forget to build e-storage but you should certainly build one as soon as your ACU makes first contact, often it's a good idea to build three or so for redundancy in case you lose one and also to help you rush upgrades.
You had lots of planes flying over his mobile AA, several unnecessary deaths there (both fighters and bombers killed this way).
8:40: There has been a bit of a fight in the middle which you have both retreated from. He has realised that you have equal numbers, so he's going for the gun upgrade. He's assisting with a couple of engies, who help repair him after the upgrade is done. If you had had storages or more pgens you would have been able to get a gun upgrade too. Aeon have two gun upgrades, and these can be devastating if you get them both.
9:40: Your reclaim is much better by this point, 2770 vs 3238, but still you haven't upgraded mexes.
11:20: He's upgrading his third mex to T2 with engy assist and plenty of mass stored so he won't stall.
11:30 - I notice you have 12 land facs and he has 8. Generally more is better, but perhaps you overstretched, meaning that any production that was not land units would suffer. Potentially reduced your flexibility, and of course the cost of extra factories will have played a part.
12:00 - Flynn ahead on reclaim, 5793 vs 4796
12:30 - attacking with tank blob vs equal or higher number, with enemy ACU w/gun upgrade in the middle. Throwing away units. You ran away tward your ACU but there were still heavy losses.
Also, I found out by accident that you can pause replays by pressing the Pause/Break key on the keyboard.
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So in summary, you lost because he had upgraded mexes and an ACU gun. Traditional wisdom has it that you don't upgrade mexes on 5k 1v1s, but because he didn't feel under too much pressure he felt he could get away with it, and he did (mex upgrade is worth ~20 tanks and takes ~3.5mins to pay off). So more pressure, more raiding and consider when you can upgrade mexes yourself. It's not an exact science but I've found you can get a feel for it.
Let me know if you want a game if you see me online.