Okay, the potty training is completely normal. Let it go - he'll figure it out. If you're working on it, stop. Sounds like the bedtime routine is a lot more of a problem.
Is this sleep pattern a new issue? Have you changed the evening routine? Usually it's advised that parents have the same routine with calming activities (for some kids, it's a bath, teeth and a story, for some kids it's not the bath because they have too much fun with all the toys. For others, calming music on the CD player works.) But he needs to learn to calm himself down without you sitting there until he falls asleep. If he learns that pitching a fit gets him what he wants, he'll start that in other areas.
For my son, we brushed teeth and sat snuggling while we read a book. He liked things in rhyme (Dr. Seuss is one example). He could pick one long book (e.g. Dr. Seuss) or 2 short ones. We sat in the rocking chair for this. He also chose who was going to put him to bed, assuming we were both available. He kissed the other parent goodnight, and then the 2nd parent and he went into his room. After he got in bed, we turned the lights off (night light on), and he decided which stuffed animal was going to sleep with him that night. I used to sing "Good night David" to the tune of "Good night ladies" and I made up verses like "Sweet Dreams, David" and "We had a good day" and put in the fun things we did together or that he did in nursery school. I just crammed the extra syllables into the verse if I had to, keeping it fairly short overall. Maybe 5 or 6 verses. I sang softly and soothingly, and ended with "Time for sleep now". My husband and I both would stroke his hair or do something else relaxing (back rub, for example). I sang more slowly as we got to the end. Then I got up to leave.
I didn't stay no matter what. Just a quiet reminder "time for sleep now" and out the door.
He sometimes fussed more at nap times, and we just put a doorknob cover on (the childproof kind) so he couldn't get out. Eventually he got tired and went to bed.
I'd pick a few days when maybe you don't have to get up early (such as the long weekend coming up) and just sleep train him like people do with infants. If he fights you, don't give in. He needs his sleep, so making him get it is the best thing you can do.
ETA - I just saw the comment about giving him melatonin. Yikes! There are very few safe supplements out there (and I'm in the business, so I know) - and there was just a report on the news last night about being very careful about where you get your supplements because most are not regulated and have little quality control. Unless you know exactly where it's manufactured and under what conditions, don't go that route! Your child's issue is behavioral and doesn't require treatment. Just because something is "natural" doesn't mean it's safe - think snake venom, toadstools, poison ivy, arsenic!