Based on what everyone else is saying, legally speaking, yeah, it's on your landlord/boss. Also sounds like youhave had at least one mutual conversation with him about you getting a significant break on rent that you "could help out" when unforeseen events (like "this") come up. Sure, there is nothing in writing, so you are not legally obligated to do anything.
We have rentals and presently have a bit of a Donnybrook going on. One house has been rented for three years to a couple and the husband is on permanent disability due to a jobsite accident. Had nothing to do with us. Rents in the area have gone up 30% since they moved in, but we have not raised their rent from the original price. So, we're helping them to the tune of that 30% that is going into their pocket (and not ours). For about the past 18 months, the renters have become very demanding that we do things/provide them with extra things that are not even remotely close to being covered in the original rental agreement, much less any standard rental agreement. We're so fed up with the bullshit that we're going to sell the house and retire from the rental industry. Frankly, we're tired of helping renters out and the only recognition we get for it is being shit all over for our efforts. And, we've been through similar situations with other renters/properties. Instances of this are happening more and more in the last five years, the last two in particular.
Again, you don't appear to be under any legal obligation, but you might want to give some consideration to the bigger picture and possibly "chip in" a little. Maybe, do the repair yourself to keep costs down. I can tell you from direct experience as a landlord, if someone wants to play hardball when I'm giving them that much of a break, there's obviously no reciprocal loyalty in the relationship and as a result, I'll do what benefits me, first and foremost. My wife and I have been doing this for 30 years. And we have pretty thick skin. But We've gotten to the point where in these kinds of situations, the decisions that we have to make are black and white and they're going to favor us.
I have no dog in the hunt and have neither upside or downside benefit potential. You do what you want.