Did i kill my boat?

Don't ask, but Basically I'm pretty sure I collapsed/fractured the internal support stringer from the bUcket to the trail on my 2008 stellar advantage layup as the hull now compresses very easily and squeaks.

Did i just kill my boat? Is it sea worthy? Since its internal, is there a way to repair? Thanks

The simple answer that I would provide from my experience is NO! My observation and experience tells me the beaded type foam used in my XT provides no structural support and is primarily for flotation. 
I bought my XT new around 07-08. Within the first 6 months I managed to buckle it and pop the seam. Turns out I l also created a leak at the venturis. In the process of repairing it I removed about three cups of sand. I am quite sure the stringer was broken and delaminated from the hull in places. It did squeek a bit after but just paid no attention. I have put it on the rocks and split the hull and popped the seam again since then. I just keep patching it up. I have paddled and and raced this boat in extremely rough ocean conditions and spent countless hours in the surf. I routinely punch through and get airborne through the back of breaking waves. I would say it has held up very well. I did tape the seam with fiberglass to reinforce it. Works great. My XT unfortunately is laid up right now after my last episode in Aug. when I dropped into an 8 foot top to bottom powerful wave at the beach. The hull at the nose was completely flattened. I have multiple cracks in the hull but amazingly none in the hull to deck seam.
The stringer is definitely broken and delaminated. I emptied chunks of foam and glue the had been rattling around in the hull for years. My current intention is to eventually repair it and go right back to using it as before. Although, the new XT sounds very intriguing?! 
I am not familiar with stellar products and maybe they're different. I have an old S. African built V10 that has a soft spot in the tail and it flexes quite a bit up wind. Never been a problem.
So, if it were me, I wouldn't be concerned about it. I'm sure others will have very different opinions.
Good luck with it.

Kill?  Probably not.  Change forever, yes, but boats are meant to be used and eventually smashed up if you're going on all cylinders...

I broke my first ski (some old SA spec boat) in 3 pieces in heavy beach break, dragged it all out of the surf, tied the mess to the roof of the car and put it back together by building a jig frame using a buddy's identical boat as a template.  My muppet show repair job added a few pounds but I got a lot more enjoyable use from it.

In some boats the strongback is important, like the stringer on a surfboard, and if compromised the hull will be less likely to survive future drubbings.  But usually this kind of punishment happens on reefs and beachbreak and such and so it's not really a safety issue.  If you are way offshore in possibly boat-breaking conditions you really should have an escort.

I say fix it!  Then every day you enjoy on the boat after that is all gravy and you won't take it for granted- like having a loved one survive a cardiac arrest...