I think this is complex, as shown by the additional information OP has given throughout the thread.
What sounded like a relatively straightforward issue about what the OH had done with some tickets (which, as has been suggested, could be reasonable or unreasonable depending on context - what type of person he is, whose fault the break-up was and how it played out, whether the friend is just a friend, lots of other factors etc.) has emerged as being about something much bigger.
I think these tickets are a litmus test of the feelings and attitudes in the wider relationship. @Pookie21, I can see why this issue would be tying you in knots if, really, it is not just about some tickets in an otherwise well-functioning relationship, but is a symbol of your fears about your OH and a test of how he will treat you now.
When we have been subject to gaslighting over a long period and are having a supposed ‘fresh start’ with a partner who is otherwise on their best behaviour, it can be really, really difficult to see things clearly and decide if a single seemingly relatively innocuous incident like this is the ‘hill to die on’, as others have put it. Often, victims of gaslighting simply cannot see things clearly. I suspect that is why you are here. While you may not decide to leave over this specifically, note it somewhere (mentally or physically), do not forget it, and be vigilant about his behaviour otherwise. Given the previous behaviours you have shared, it is highly unlikely that your OH has reformed, or would be able to reform without serious work, therapy etc.
If you can, I would suggest trying to mentally step away from the question of the tickets and examine how you feel about the bigger picture. Tickets aside, what does your gut tell you? Do you feel loved and supported? Do you truly trust that your partner has changed? Do you think this partner is worthy of you or do you deserve better? Do you think you will look back in five years and be glad that you gave the relationship another go, or do you think you might wish you hadn’t wasted your time? What would you advise a friend in this situation?
Some posters have advised ending the relationship, which I understand, but that can feel overwhelming when you have been manipulated and abused. Sometimes people need to detach themselves from these situations by degrees (assuming there is no threat to safety which warrants breaking things off immediately). It sounds like you already detached yourself once by breaking up - well done. You sound perhaps less invested and more wary now than you were previously- which will ultimately make leaving easier. At this stage, as long as you are safe, it doesn’t have to be all or nothing. As you don’t live together, you could tell him you need to take a pause or break while you think about whether you want to continue. If you do that, his reaction will tell you a lot - is he accepting and understanding, or does he lash out? If you decide to continue after some reflection, it could be with different or stronger boundaries, or you may decide to end things. Again, his reaction will be telling.
I think that the tickets are just a canary in the mine, so to speak. Good luck!!