I get boners when looking in mirrors aswell - all the time. Its completely normal.
Showering with other guys naked is quite unconfortable, but you will soon find that it will become very relaxed and easy. Feel proud that u have the 2nd biggest erection.( i know i would)
Almost every1 goes through a phase where they think thery are gay. You'll just be curious lik most teenage guys (me included)
Your 13, thers no need to worry about develpoment, everything will soon grow. dont worry!
This is Big Brother,
could all Housmates please gather on the sofa