Lasting Relationships

What does it take to create a lasting relationship? Should it have to be a lot of work? Should you get mad at everything that person says? Should you question their motives all the time? I know I have the capacity to keep my relationships for a long time. My closest friends are relationships that have been 13+ years for the most part. I don't see these friends that often, but when we do see each other, we pick right back up where we left off. It's easy. Natural. And surprisingly doesn't take that much time to make it work. Is this a bad thing? Should I be putting more effort into it? Am I offending them that I don't talk to them every day...or even every week at times? Am I a bad or uninterested friend because often we might only talk once a month? Truthfully, I am pretty much unavailable Monday - Thursday except by email. My weekdays are full with 11 hour workdays, an hour commute (total) and trying to get to the gym. And, apparently the older you get, the more your weekends book up, too! So, yes, I am busy. They are, too. Getting together is getting harder to do. (The Dr. Seuss ryhme was NOT intentional! LOL!) I don't want to have foot-in-the-mouth disease here, so I don't really know where to go with this one. It's just what's been on my mind today.