best friends girlfriend

Ok, in grade 6, I was best friends with this girl April, and this guy Luke had a crush on her. All 3 of us went to different schools, me and April grew apart, but me and Luke grew closer. Me and Luke are now best friends. Since then, April asked out Luke twice, but has broken up with him within 2 days both times, leaving him completely heartbroken. Of course, being his best friend, I took care of him. Her reasons were always pretty sketchy. she always liked someone else or ‘wasn’t ready’. Either way, he always said he’d be an idiot to be with her again, and I agreed. But now, 2 years after they broke up last time, they’re together again. He’s gone from laughing about how shes nothing more than a pretty face, to being in a relationship with her. I have a massive problem with this because I don’t trust April at all after she hurt him so much, and suddenly Luke doesn’t even care about me or what I think about anything which is even worse. I’ve always been supportive, but we’re in 11th grade. We’re not 12 years old anymore. Being a good friend isn’t always about being supportive, it’s about being honest and I can’t seem to get him to understand that all I’m doing is being honest with him. 2 months from now he’s going to end up in bed listening to James Blunt and Jeff Buckley cds on the phone to me, and he doesn’t get it; he’s set on making this work even though we established a long time ago that it doesn’t. What can I say to him to make him understand that April hasn’t changed?