Could you expand on why you think Arianne will marry Aegon? When reading Arianne II it seems that Elia Sand is the more likely to get involved with him, based on her defiant personality, impetuousness, and exploring her sexuality. Arianne is more consumed by maintaining her status as heir to Dorne and wondering if Quentyn’s return would change anything. And Connington would never allow it; Aegon’s hand needs to be kept open, so if it happens it’s probably in secret and done quickly.

Arianne wants to achieve her father’s ambitions of destroying the Lannisters – “my father entrusted this task to me” – Aegon has an army in the field and is marching on King’s Landing right now.

Arianne doesn’t like the idea of King Quentyn – “will I need to kneel to him” – marrying Aegon makes her Queen, just as Doran had intended with his marriage pact to Viserys, and cuts out Quentyn too. 

Connington wants to keep Aegon’s hand open for Dany, but Aegon might not agree. Aegon’s whole deal is that he’s aggressive and ambitious and isn’t willing to wait – here comes Arianne Martell who has armies now, not “one day.” He’ll overrule Connington, as he did with Storm’s End and with Rolly, and he’ll use Arianne’s spears to take King’s Landing, seemingly vindicated. 

And then Dany will show up. Aegon might offer her a tripartite marriage, but she’s not going to be interested in negotiating.