Need help confessing

I've been thinking about this for a while and I've decided I need to confess (again). I confessed when i first had a crush on him, before we became friends and it was a more nonchalant thing. He said he didn't want to date someone he was friends first.
Over the last 2 years, we've become friends (mostly through mutuals and group stuff). I realized recently that I have feelings again, which are definitely more serious. I was told by a mutual that after we hung out for the first time alone last week (farmers market trip), he asked his friend if they thought I still like him. The friend said it was possible, but could go either way and asked what he thought. He said he "had never thought about it before" and that he likes spending time with me. Knowing him, he probably didn't give it any more thought past that .
Even though I'm pretty sure he doesn't feel the same way, I need to get it off my chest before he graduates next month and leaves for his job. Any advice on what to say? And how I might be able to get him alone without setting off the alarms in his head?