I was for Aaron and Emily in S1, but since it never happened for the reason that was never explained in S2, I found Aaron and Isabel an interesting couple although they would have been more interesting if we had been shown their romance from the beginning.
Somehow Isabel reminded of Alex Kirkman: she was more radical than Aaron and she didn't hide her opinions but tried to influence on him via "the kitchen way". At first it seemed that she didn't understand the political realities that Limited Aaron's action but in the end Aaron was shown to have been too cowardly, or rather thinking too much "inside the box". In short, she challenged him in a good way and made him a better man.
As for Aaron's identity, since they were living together, of course it was also her business. By changing his name, Aaron had denied his roots and pretend to be somebody else whereas Isabel had chosen the harder way. I don't blame on Aaron who of course had a right to chose the method he thought was the surest way to succeed, but in the end he only succeeded in the elections because Isabel guided him to embrance his heritage and to become the champion of those who couldn't choose.
It was interesting to compare the three couples in S3. In the beginning Mars and his wife seemed to have most problems: the wife was an addict, Mars had an long affair and they even admitted that he had married her in order to succeed in politics. Yet, they seemed to be happy in the end - unless Mars didn't just pretend and manipulate his wife to run because he and Kirkman needed support in the Senate.
Also, concealing the HIV in the beginning of realationship seemed to be a deathknoll in the realationship, especially as it was an elemental breach of trust, but in the end the tube vizard and bodygard seemed happy too.
On the surface Aaron and Isabel seemed to have least problems but it was just they who didn't succeed. Yes, he cheated her but it was only one night and it seemed he right after it repented his mistake (perhaps the greatest mistake was to confess?). I can understand Isabel's charge that "you don't take me seriously" and there was really cases Aaron didn't but there was also cases he did. Maybe it was really a difference in age and status that separated them?