I'm not sure what to say

Sara • I’m a 24-year-old graduate student working on my master’s in social work. I got my bachelor’s in psychology in 2015, and I live in a tiny apartment with my wonderful fiancé. 😊
My boyfriend and I have been dating for about six months. We want to get married eventually but haven't officially declared an engagement and we're both okay with that. I'm 22 and graduating college in December; we met at school because we both attend here, but he's a non-trad student at 30 after being in the army for a few years. He keeps talking about he is gonna fail out of college and how he's tired of scraping by with his grades and I don't know what to say to him that will help him believe he can make it through the rest of his college career (he's only just started his sophomore year). I tell him he's smarter than he thinks and I believe in him but it doesn't seem to have much effect. Any advice ladies?