Do you have a trailer at your place to work with him, or have access to one to work with him? The most important criteria you need is patience, for your safety as well as the horse's. Patience, gentle coaxing, no pulling, no pushing. Unless you stop everything you've already done, your problems will likely get worse.
Is the trailer safe and large enough for him? Straight load, slant, how big?
Is he being loaded with other horses in the trailer or alone?
If you have a trailer at home to work with him, or can borrow one and can feed him inside the trailer, that is one way to acclimate them to loading and unloading themselves almost automatically.
There are lots of reasons why horses have bad experiences with trailers, and I don't know how long you've had him/her or what you know about the history, but the more you can find out the better and then see what you can do to make a negative experience one that is positive and something to look forward to.
Have you put any hay or grain in the trailer to gently encourage the horse to come in? Even so, sometimes they will still bolt once they're inside and they panic. There can be a myriad of reasons for that.
Sometimes not tying a horse is safer, depending upon the trailer, and every situation is a little different. Some horses hate to be tied and in the right trailer and with safe driving will ride better loose and prefer to ride with their butts to the front of the trailer because they balance themselves better.
There are so many things to consider, and if your experience is limited it's important that you be safe, and if you can find someone to help you who is patient and doesn't try to bully the horse in, I hope there's someone available to give you a hand there.