prayer for a friend

My best friend at college has a WONDERFUL loving Christian boyfriend of almost... 4 years I believe. The two of them are wonderful together and eat sleep and breath Jesus love. However, they have premarital sex... And lots of it. I know the two of them believe (and even I do) that they will be married and spend the rest of their lives together. But sex before marriage is sex before marriage. I am asking for prayer that she and he both feel convicted when it comes to acts like this. They're a wonderful couple and I pray that they abstain until their wedding day! Also prayer for how I can be a sister of Christ for them on this topic... I feel so awkward, even though she's my best friend, to bring up how they shouldn't be having sex... Maybe I shouldn't say anything. I'm a very new Christian and she has taught me a lot so I feel weird it coming from me... any words of wisdom from a clueless best friend would be greatly appreciated!!