I would encourage you to think about the worst possible outcome and expressing your concerns to your Head, The Chair of Governor's and your Union.
It is clear that your colleague is in crisis. (How deep a crisis, I don't think you can gauge.)
I have just extricated myself from 26 years of teaching and during my career, I have been touched by 7 suicides. (1 family member, 2 friends and 4 colleagues.)
The four colleagues were ALL teachers.
Teaching has become INCREDIBLY TOXIC and I'm not sure that SLT actually care anymore about what is happening to the vast majority of classroom teachers.
First thing I would do is take tomorrow off. There is NOTHING that is more important than your own mental heath. Don't just struggle on until the end of term. The system is broken. It will only be fixed if you show that it is broken.
Secondly, I would send an e-mail to EVERYONE who you think might listen. SLT, HR, Governors, Union etc. EVERYONE needs to know how concerned you are for your colleague. Be REALLY explicit. You could save a life.
There will be people on this forum who will say... "No-one has mentioned suicide" "surely its not that bad" "You just need to get to the end of term and have a nice break" BUT I would guess that this situation isn't going to be resolved with a week away in Majorca.
One of the schools I know is currently having to give evidence in a suicide inquest. Witnesses are being called, paperwork checked and arses are being covered and scapegoats found.
Be brave and step up. Don't let it be too late.