I'm first going to ask that you not yell at me because I know I did things wrong.
Hey, sounds like you're doing well on your way to getting things worked out anyway & have a good attitude about it
, but remember, if you feel 'yelled at' here, it may be just people giving strong opinions sounding abrupt because writing lacks tact of face-to-face... & if people really are truly being rude to you, still don't take it personally because that's their problem, not yours!
because the hackamore multiplies the force put on a horse.
I'm guessing you're talking about a mechanical leverage type bitless. Yes, they can be very strong & also unclear to the horse. They're not generally great with direct reining, for eg. But changing headgear/feel/cues isn't just about application of pain at all - true hackamores & halters for eg can make a great difference to a horse that's 'bit spoiled' just because they have such a different feel, so don't 'provoke' the automatic responses the horse makes with a bit.
Have been riding him In a round pen in circles with the snaffle. This horse
Very good idea IMO, to keep to a 'safe' environment.
That way, you can practice asking for responses without worrying about the horse running away with you. I'd personally suggest you keep to enclosed environments until you're going well & reliably, although a round pen may be too small after a bit & remember 'improved' behaviour will not automatically transfer when you finally go out, but will certainly help you & your horse be in better 'synch'.
My thoughts are to sell my horse to a person who will be able to do things right without hesitation and get an easy going horse and start off right from the beginning. Not let it get away with things but yet if things do get bad to get help.
That sounds like an entirely reasonable option. But this won't help you learn to do better & you may not find yourself a better horse - the devil you know may be easier than the one you don't. Not blaming for this - none of us are born understanding & much of our knowledge comes from making mistakes - but it's highly likely it's the way you're riding & using the reins, etc as to the behaviour of your horse.
So I'd personally suggest you find a good instructor/trainer to give you some lessons & help show you how to turn around your relationship with him. You & they may come to the conclusion after a lesson or 2 that you & he are better off apart, but then again you may find that he's the perfect horse, with some different tactics up your sleeve.