I rather liked this one and the concept of the guy going to surprise his girlfriend and school and finding she has moved on from him. I like the play with the girlfriend and roommate in her apartment and how the roommate drops him off to see him find his girlfriend giving her casual date (really not) a BJ, with her then adding him to the mix. Love her casualness as she flushed him away the next morning. 

Just a great plot. I might have written the ending differently - the whole toughness of the tiny could have had a loophole to the effect that if they are swallowed with other food, the stomach acids activate to work in overdrive and overwhelm the toughness of the tiny (whereas, if they were swallowed alone, they would be tough enough to survive the digestive process and make it out alive).

I can't say I'm a fan of the ending.  But I take some solace in the thought that if a shrunken person can survive digestion, then its likely he can survive being flushed and some time in the sewers.