If only Isabel and Alex had more screen time then I am sure you would see a whole lot more Stargazers in the crowd and more Adult oriented stories.He would always be something stable in her world, no matter how messed up the rest of her life might become, another thing Isabel craved. Besides, he accepted her just the way she was. He never tried to change her, even when she wasn't exactly treating him all that well. I think in her eyes, he was simply perfect.
There are quite a lot of Mature stargazer love scenes out there. You just have to be willing to read M/L and M/M fics to get to them.

Kara