i'm not sure Simon's behaves poorly at all in the show. she was gone for a long time in atlantis - he KNEW she might not ever get back. sure, she'd been away for missions before, but with the possibility of contact, and a definate conclusion. he always knew that if she died, he would hear and could mourn and move on.

in the video she leaves in Rising, she warns him it might be a one way trip. i saw that first video as a preemptive breakup - a "hey, btw, i might never see you again. i love you, but i love this more. feel free to move on." in Letters from Pegasus, she sends another message, saying the situation is WORSE. not only will she never get back, but HEY! they're about to DIE! horribly!

were they actually living together? that romantic scene seemed like "this is the first time i'm seeing you since i got back from my intergalactic travels! let's have reunion sex now!" moment to me. it's likely that she was kept so busy at the SGC that she might even have been staying there. if that was their first romantic encounter after her return, i can't blame him for not mentioning it earlier.