I find it quite shocking how many people are attacking you for being 'jealous', 'insecure', 'not trusting ' etc! IGNORE THEM!
Firstly, as women we need to own the sh*t out of our NATURAL emotions! Then REGULATE them! Your feelings are so dam n natural! I am as secure as any woman can be with my husband! But if put in this situation, God I would probably get sick with worry and anxiety IF I VALUED MY MARRIAGE which I do, and clearly you do too!
I would simply talk to my husband about it and expect him to understand and reassure me of HIS LOYALTY to me and our marriage. Your husband is not superhuman nor an angel and this woman has no reason to respect your marriage! And your relationship is still so very knew, despite being married. We can all be a bit doubtful in 100s of situations. Anyone who acts like they're in a saintly marriage with ZERO insecurities; feel bad for them for putting so much pressure on themselves and their marriage to appear oh so perfect.
Your husband gave you details that clearly show they (him and the other woman) didn't have any real issues, or closure. So your concerns are valid as can be!
When you feel reassured, you then have to put in the work to let it be and not pay mind to it, unless he gave you a reason to be doubtful or suspicious. Your husband sounds a bit like someone who may crack a joke here or there without realising the insensitivity of it and how much that would trigger your anxiety and send your insecurity through the roof. So lay a little grounding on how joking about the situation and any mention of her is off limits. If he respects you enough, and is willing to understand you, this should not be a big ask at all.
Lastly, sorry you're in this situation. I can imagine it sucks. But roll with it, manage it, and keep it moving. We all get tested, as does our marriage, and no one likes their tests. This happens to be yours. You got this ;-)