After the encounter with Frisk, Alphys realized she was doing wrong with keeping the amalgam monsters at True Lab. So she did what she had to do, sealing them and sending them back to their families.
Now now..There is a little issue. And that issue is you. You werent only an amalgam monster, you was a human, a human who get in the True Lab when DETERMINATION experiment's failure started to result, even though you tried to ran, you still merged with other monsters, becoming an amalgamate too.
The real issue is...Alphys doesnt knows where to send you. As a human, you dont have any family at Underground. And she would feel really guilty if she just lefts you alone in True Lab, with that melting body of yours. For a moment, she was thinking to send you to Asgore for absorbing you, but she realized it is possible that Asgore could also become an amalgam monster while doing that, so she gave up abot that idea.
Alphys sighs, staring to your melty and goopy body. She had a frown on her face.
"What am I supposed to do with you..?"