I wrote this as a reply to @ct-0451 's post but I'm greedy and I liked it enough to want a copy of it on my blog.
A quick summary of what we know about the marriage from the quick exchange in ep 8:
- we know it was likely an arranged marriage, per traditional chandrallan customs
- we know they were fifteen when it happened AND
- we know that when she was talking about perrin at 15, mon mothma called him "the firebrand of the academy"
And it's so painfully easy to imagine Mon mothma meeting this brash, loud, irreverent boy her parents have chosen for her, and mistaking that temper and energy for the same passion that makes her radical.
And then they go to Coruscant and it's scary and different and there's only one person who feels like home... But you have each other and you're both young and excited about the world. And so it does take years for that shine to wear off, for both of you to look more closely and realise the other isn't who you thought they were.
All of which to say I think it was an arranged marriage and I think it had good years, and that makes it sadder for Mon mothma as she watches it crumble away.