Southwest Airlines has had a long love affair with the Boeing 737 aircraft. In fact, the airline's extremely successful business model was built around the 737. It's currently the only plane Southwest flies, which makes training, maintenance, and operations less costly than airlines that fly a variety of different aircraft.

It's no secret, however, that this love affair is being tested with the ongoing grounding of Southwest's fleet of 34 Boeing 737 MAX planes (United Airlines has 14 and American Airlines has 24). Yesterday, Southwest CEO Gary Kelly revealed that the 737 might not be its forever plane despite their almost 50-year-long relationship.

In an interview on CNBC yesterday, Gary Kelly said,

The [737] MAX is a small percentage of our fleet, fortunately, and our folks have worked very, very hard to manage through that. So, my hat's off to 'em--they did a great job.

When host Jim Kramer asked Gary Kelly if the company might ask for reparations from Boeing for the financial damage the airline has suffered due to the grounding of the 737 MAX, Kelly made this surprising statement:

Well, yeah, we're an all-Boeing carrier. We're an all-Boeing 737 carrier. So, that's who we are, that's where we are. That doesn't mean that we'll be an all-737 carrier into perpetuity. But that's certainly where we are right now.

Southwest CEO Gary Kelly went on to say that his company's negotiations and relationship with Boeing was something he would take up with the aircraft manufacturer privately. Continued Kelly,

We have a great, historic partnership with that company, and I would expect that would continue going forward. But, yeah--we've got to work through this MAX issue. When we launched the MAX airplane, we felt like it was the best single-aisle airplane in the world, and we still feel that way.

In a presentation to a Dallas business group last week, Gary Kelly said that Southwest had no plans to change its order with Boeing for more than 200 additional 737 MAX airplanes. However, it was widely reported that a Southwest team recently visited a European airline to take a closer look at their Airbus A220 aircraft. Kelly reportedly said that the timing was "coincidental."

But, the question remains: will Southwest's customers want to fly on these airplanes once they're back in the air, or will they seek out other airlines to avoid them?

While that remains to be seen, it must be a concern for every airline that will one day once again fly the Boeing 737 MAX.