Gotta have trust and communication!
So many relationships deteriorate because of trust and communication. I've been watching my best friend's relationship do this for the last three years. And they're planning the wedding right now.
Normally I would say to stay out of it, but it was breaking my heart and I just paid $300 for the maid of honor dress, so I'm going to wear the thing. Since they're both my best friends, I staged an intervention. We hashed some things out and the two are on their way to working their problems out. Both have certainly been a lot friendlier - much like their normal selves.
Their problem was a lack of communication had fostered mistrust. It's the little things that seem to make the biggest differences and he believed one thing while she was adamant about another. Communicate!