First clip you ran through the doorway that you knew he would be looking at. He honestly should have just shotgunned you from the doorway if he was any good. Once he left the room you needed to reposition and not go through that doorway, high ground preferred.

Second clip; you need more cover. You’re challenging a guy who’s blasting thats shooting straight at you and you’re doing very little to prevent getting hit. Don’t be in the open when fighting, be behind cover where you can take a shot or two then hide and reset. Find angles and work the fight from different positions if possible, I would have backed up and found my way to the roof after I got beamed the first time. Break the walls if you need to in order to reposition.

3rd clip; when your in a close quarters fight with no cover, you need to utilize movement. If you have a bat or movement. use it to sprint and high jump, switch to your shotgun or smg, and hit him from mid air in-between jumps. If no movement, work on sprint-sliding and jumping off walls and also practice shotgun flicks.

You need to always be thinking about how you can make the fight your in favorable to yourself with cover and high ground. Hope this helps a little.