I think if you read the posts by MeasuredApproach earlier, you'll find some pretty good examples of why Scottish, Irish and Welsh resentment isn't simply because of things that happened hundreds of years ago. It's also because of a sense of unfairness relating to the current system in the UK and the place of the other three nations in it. There are lots of reasons, some subtle and some more evident, that contribute to feelings of resentment in the other three nations. As others have rightly pointed out, prejudice is never acceptable. But it is also true that whitewashing history or ignoring the impact of a privileged position in a current situation is not acceptable either. The UK, as a whole, but specifically England, needs to really explore these feelings and the reasons for them before they can be addressed.
Your whole comment, @MrsHuntGeneNotJeremyObviously, is reductionist. You are attempting to reduce centuries (including very recent history) to a few simple facts instead of looking at it hollistically as the extremely nuanced and complex history that it is.
For example, much recent Scottish resentment still stems from the Poll Tax, which was imposed on Scotland a year earlier than anywhere else in the UK by a government that Scotland voted very decidedly against. The Poll Tax ruined families, and the resentment is very real. Of course, that should not transfer into resentment towards a single person because of their nationality - doing that is always wrong- but there is a right there to feel resentment. It also true that the union with England, which at the time was incredibly unpopular among the general public, led to Culloden and the mass slaughter of thousands of people, the end of the Highland way of life, a literal ban on culture and the destruction of language.
I understand your perspective about class, and I also agree that many problems are due to a powerful ruling class. However, it is also reductionist to say that it is only about class - it's not. The political system in the UK is a major problem. It simply does not work for all of the constituent nations equally, and it breeds resentment. In my opinion, this is understandable.
With regards to the independence vote, as you say, the vote is just a snapshot of opinion at the time. Opinions change, and of course votes can be reheld. Not every week, but people change government (because they change opinion) often every five years. If the Scots' opinion has changed, for example because of Brexit (another example of how the UK political system is unfair and breeds resentment towards England), then of course there can and should be another vote. It's democracy. The Swiss have referendums four times a year.
However, that's off topic. I want to just end by taking issue with your "stop acting like a victim" comment. Again, it's reductionist. The UK and the relationships between the four nations are extremely complex. There have been many instances, many of which are in very recent history (i.e. Brexit, the Poll Tax, the British involvement in The Troubles, and so on) where people in the other three nations have had a legitimate right to feel angry, ignored, disrespected, frustrated, and, sometimes, victimised. Telling people just to swallow that and forget about it is ridiculous.
The only way to deal with prejudice is for there to be openness, honestly and a genuine conversation on all sides (prejudice is not just limited to Scottish people against English people -it can and does work both ways). With the kind of attitude that you have, that will never happen.