At first, I would just spend time with them. He would follow me around and try to bite me. .... He told me to longe him and get tack on him right away. The trainer was very tough on the horse and told me that I had to be because this horse is soooo stubborn and dominant.
I was one of those to suggest you build a good relationship first, but that's not to say you allow him to boss you round & treat you like another horse. With a personality like this, as suggested, I'd be inclined to start from the other side of a fence & teach him 'manners' first. You don't have to be 'bossy' yourself, just consistent & firm & teach him what behaviours work for him(he's rewarded for) & what behaviours never work(he's not reinforced & there may be unpleasant consequences... such as no feed for 'rudeness').
As for this trainer, everyone has different opinions & experiences. My own stem from studying behavioural psychology, equine ethology & behaviour, and working with, among others, with a number of 'damaged', 'untrainable', 'vicious', etc, etc... horses. I have come to believe attitudes such as this trainers, and the methods they tend to employ are unhelpful and often further damaging to the horse & his ability to become tractable. They tend to often further cement any negative attitudes & behaviours in horses of strong personalities. Then the horses get further labels as 'untrainable', 'vicious', etc....
As I tried - possibly badly - to explain, I believe it is important to *avoid* being confrontational and aggressive yourself towards the horse - be it with direct physical punishments or attacks, or with the 'work' you 'make' the horse do. Instead, finding ways of making the Right things actually Good Things, so they 'work' for him and yourself. Instead of going into battle with him, find ways of giving him what he wants at the same time as doing as you want. Part of this is starting small & easy, not just rushing into lots of hard work. When you get as far as what you now perceive yourself as 'work'(if you think of it as that, how does he see it??), try to ensure it's actually 'play' for him.
Of course, this is only my opinion, but that's all anyone can give you.
When I visited him today, I had a "lead horse" walk, erect shoulders, looking forward, walking with purpose. I made him respect my space by not letting him crowd me. He respected my wishes. Then, I walked over to him, put the lead rope on him, walked off without looking back at him and then, asked him to whoa, and petted him when he did what I asked. Finally, I tied him and petted him gently with long strokes for 10 minutes. He just stood there quietly, moving only to shoo flies. When I released him he didn't try to bite! I don't know if that is progress. It is stressful to me to have to be that way. I like to be relaxed around horses and just let the relationship be natural. Will it always be this way?
I think yes, if you're confrontational about it, it will always be that way. He may accept you today, but decide he's up for a challenge tomorrow. If you want to use the 'dominance theory' in practice, you'll only 'win' at the expense of his 'loss' and if he's so assertive & playful, you'll always need to watch your back. - On that note, I would not turn your back on him, walk in front of him, particularly at this point in time. You should be driving him, or at least leading from beside him. For one you can keep your attention on him & gauge when he may try something & secondly, alpha horses generally 'push' their herdmates along, so don't let him get more practice at pushing you around. If on the other hand, you quit challenging him, you should be able to develop a mutual arrangement.
NB my attitude may sound all soft & fluffy, that I let horses get away with stuff, but I am quite firm & will not tolerate 'bad manners', etc. It's just that I approach it differently to some.
I really don't think that horse likes me???
I'm not surprised, as it sounds mutual & you don't seem to be trying to be liked. Sorry if that sounds harsh, it's just the way it seems from what you've told.