If you don't learn from your mistakes it will be frustrating I guess. Don't make excuses when you die. The other guy might be high level, he might have looms, he might be a "pro", but there should be beyond that an ultimate reason for your failure. If you keep trying to work that out then you will improve, if you dwell on excuses you will probably just keep repeating the same mistakes.
Use ` a lot..I mean half the time you should be looking while holding this. Look for cav, look for enemies, whatever. You might want to bind it to another key. I like to use my thumb since other than that its only used for jumping
Don't go and 1v1 if you don't feel confident you can take someone on 1v1.
Learn who certain players are from their armour or weapon type and know when you have 0 chance against them, even if you are 2v1 against him
Learn to defend yourself early on. Either manual blocking, dodging, whatever
Stay with your team at all times
Get a sense of how the battle is progressing. When to attack and when to defend. If you attack too early on and die you are now completely useless to your team. Just stay alive as long as you can while still keeping a sense of when you will be best off going and helping other players. Even if you are a distraction you might be able to get an enemy to show his back to a team mate.
Play very defensively, even when you think you have someone outnumbered. Players love to target switch to people they think are weak when you least expect it
Don't be afraid to block twice or more in a row. Sometimes you think you have an attack window but without timing people will attack again before yours will hit
Learn which attack to use at which time. Each attack direction has its own advantages/disadvantages
You could try to get your own support role in the team. this way you help your team, but you also have an outlet excuse for when you fail (you aren't there to 1v1 etc). Like anti cav polearm, long range polearm (stay back and try to hit enemies from beyond their range) or hoplite. Anti cav ranged (shoot horses all round). Thrower, crushthru str crutcher, whatever. If your build isn't designed necessarily for 1v1 then you might not feel so bad when you die
Learn some good builds and specialise with what you learn as a player, and what skills/stats you get for your character. If you always play 1 build type you can nail that area before moving on to other stuff. Try balanced builds before going too far str or agi imo
So much to learn in this game, but if you actually are learning as you play then you might enjoy it more. Half the fun for me is trying to get better, and you will if you keep practising.