Stop.
Save up and buy either a Ruger MKIII or Browning Buckmark .22. go back to basics.
Stance; it's not rocket science and it's over done/over thought by many. Shoulder distance with left foot further forward. leaning forward from the waist ever so slightly, not back.
Sight Picture; for defensive shooting it's all about point shooting. For groups, it's all about focusing on the front sight. This is the number one/main/most significant aspect of any tight group. Back sight should be blurry, the target can/might be a bit blurry but that front sight should be crystal clear. The mind is good at lining up the back sights or a peep sight but it needs that one focal point to put it together and that's the front sight. If you don't do anything else, this is the most important.
Breathing; Stop; don't hold your breath, just stop breathing when your lungs aren't too full, not too empty and time it so it's natural and a second from when you believe you're going to fire. If you stop too long then by default you're holding your breath. Just stop as the finger is squeezing the trigger and the front sight is coming into focus.
Finger: squeeze, with the pad. If youi're only using the tip that's no good. If your finger is buried and the trigger is on the joint that can be a problem. Key is to squeeze. It should surprise you but if you're focusing on that front sight the with all your intensity (and keep focusing after the shot) it'll work.
Hearing; double muff. Put some ear plugs in and then head muffs so it's really really quiet. A good technique for new shooters although it makes range communications hard. Everyone reacts to sound. It's how God made us.
Grip, for revo's hight and tight and I mean tight, for autos you don't have to be choking it so bad.
Caliber; .40 is a snappy son of a gun. I think it's one of the best SD rounds out there but it's difficult to shoot well and I think a lot of people won't admit how badly they shoot it becasue they've bought it already and so what are they going to say?
Truth be told many folks would be better off stepping down to the 9mm or even stepping up to the .45 that has more of a push/thump type of recoil versus a snappy crack type recoil.
Finally; relaxe and give yourself a break. Pistol shooting isn't easy. We've all be ruined by hollywood. It's actually hard on a good day and real hard on a bad day.
start reading and learning about point shooting. Try to get a realistic understanding of how you're likely to deply that handgun in a civilian SD situation. 99 out of 100 you won't be using sights. You'll be fortunate just to make up your mind and to be able to bring the gun to bear in time.
Practice unloaded presentations of the gun and practice point shooting. Think softball size group COM (Center of Mass) at 7 yards. Then work to do that moving left and right as you shoot or retreating. But that's all for another day.
Get a .22; $300 or so and you can shoot all day long and work on the fundamentals in a way you can't with a .40.
And although I agree that dry firing has it's place, I believe it's WAY overrated. It's just not the same as shooting a gun with a live round. It's just not and never will be. there's no noice and no recoil. I won't argue with anyone but to me it's way overrated.
When I'm shooting bad I go back to the basics I learned almost 40 years ago...
front sight, front sight, front sight, front sight, no, I'm not kidding, front sight, then breath control (stop don't hold) and a gentle squeeze.
And walla, you'll have it!
God Bless
Gideon