It's Him.Again.

This year his locker behind mine. We have a very small space between each other. How do I start a convo.?

Well you seem nervous about talking to this boy so after one of your classes that you get together why don't you go up to him (preferably when his friends are not there) just talk to him start by asking him something simple like what is the time and take the time to introduce yourself if he doesn't know who you are. For one second forget your feelings for him and pretend you are making friends with a stranger. Just act confident when you speak to him and be nice to him, try not to come on too strong you might scare him away.
Good Luck Sweetie :-)

If the guy is interested, anything you say will start a convo.

How about, "Nice locker?" :-)