Remember when electronic mail didn't exist and had to rely on telephones and in-person conversations? Embrace that era of being less connected now, because your Gmail is probably not really working.
The Google team is ON IT, however, and has been updating the problem here—around 2 p.m. things sort of took a turn for the worst, and they informed the masses that they are continuing to investigate the issue, which has become more widespread since this morning when it began. At 2:05 p.m. it was affecting around 50% of Gmail users, who are receiving emails hours after they were sent, or not at all.
On the upside, that guy you were enjoying a casual back-and-forth email flirtation with probably wasn't weirded out by your last reply? His email is probably just in the electronic purgatory the rest of our emails are in.
UPDATE: They now "expect a resolution for all users within the next 1 hour [so, around 4 p.m.]. Please note this time frame is an estimate and may change."