I don't get the urge to masturbate when my room mate is around but when he leaves it all comes back

Anytime my roommate is around (could be for weeks, I don't get the urge to but immediately he leaves; I can fight the urge for a day, but the next day I get exhausted, sad, and stressed and eventually gave in.

I don't when I'm very active and have things to do with purpose. My downfall is always what I picture in my head.

What can I do to stop this?
I'm tired and I Don't Want This Anymore