[Cool]

If this is the first time this has happen don't over think it. Look at all the factors to why this could have happen.

-Stress or/and exhaustion set in becasue you was looking at the clock
-Has you been masturbating for the past two week w/o your GF, you might not have been in the mood.
-Did you think yall HAD to have sex because its been two week?

I too have not cum for one reason or another i just let some time past take a shower and a nap then try again.

Side note: Try masturbating with your GF see if that helps.