I'll watch the replay and give some notes.
Your MG is north where your MG bunker is for like 20 minutes, you could have had the MG move and had a much easier time vs the inf blobs.
You built a stug when you didn't really need emergency AT, if you had just banked fuel and then let your friends panther fight the brit tanks your opponents wouldn't have had such a good start in the armor war. Then your friend throws his panther away after killing a sherman for free!
It may not feel fair, but frankly the allies can throw a few tanks away while the germans have to make sure not to lose many (if any). Just like real WWII. They also had 3 fuel OPs while you guys had 0, so once you lost those first few tanks you were pretty much screwed. Check this out:http://imgur.com/a/Aimbe
You also both picked doctrines very early, and neither had a super-heavy. A jagd, a tiger, a command panther, any of those would have helped tons. Also if your friend had gone command panther you could have used flares and realized they had no inf in the mid game and there was nothing stopping you guys from pushing up into their base.
TL;DR: The comets were unchallenged because you lost tanks early unnecessarily, didn't build fuel OPs, built stugs instead of teching T4, and neither of you picked OP commanders.
GL in your future games!