Here’s why Keith was so willing to sacrifice himself for the sake of the team at the end of season four:

• He’d rather lose his own life than risk losing someone that he loves again
• He believes that his life is expendable

Keith does not have anything to go back to outside of Voltron, they are pretty much his only family and home

He’s also an orphan since he lost both of his parental figures when he was young. And we already know how much of an affect losing the people he loves has on him. Take Shiro and his mom for example

His mom abandoning him at a young age caused him to be untrusting and distant like he said. So to somehow build a bond with new people like this enough to feel like they’re your family, that’s obviously really important to him

It clearly even hurt him just to leave them behind to go on the mission with the BOM, no matter how much he felt he needed to

But when he sees that the only family he has left is in danger of being killed, he’s willing to sacrifice it all to save them because he literally probably would not be able to go on if he lost everyone on the team like that. He’s already lost enough in his life, without them he truly won’t have anything

Keith already knows the life Hunk, Pidge, and Lance have back on Earth and that Allura has Coran back at the castle, while he just has an empty shack waiting for him in the desert. And we all know by now that he would never let anything happen to Shiro, the one person that has always been there for him the most and that he will always protect

Keith believes that without them he will have nothing to live for and that they deserve to keep living the best lives possible, to have some sort of future. He just really wants to save them I feel, and if he has to do that by taking his own life he won’t hesitate

Keith probably also felt that since Shiro is now leading and Allura is in Blue, the team is full and he isn’t exactly needed, which is why he chose to move forward with the BOM and is easily risking his life here

EXCEPT KEITH DOESN’T REALLY SEEM TO REALIZE HOW FUCKING IMPORTANT HE REALLY IS AND HOW MUCH OF AN IMPACT IT WOULD HAVE ON EVERYONE IF HE DIED, SO IF HE EVER TRIES SOMETHING LIKE THIS AGAIN I WILL SERIOUSLY-