Here's my two cents: I used to be a nursing assistant. I did that for about seven years. I had to quit and change careers eventually due to burn out, stress, not wanting to be complicit with the ugly side of health insurance, etc.
After I quit I found that I had a lot of trouble feeling compassionate towards other people i.e. compassion fatigue. I had spent so much time and energy with so many people with extremely bad health, many of whom didn't really have a hope for recovery. It's like my compassion was used up and here it lay now like a strained muscle.
There are a lot of different angles to it. For one thing, it can be hard to identify with other people who aren't from that background when you've been in medical for so long. Other people complain about so many little things while I spent years helping nurses bandage bed sores, toileting people, washing dead bodies, talking with people about their own mortality, etc. After that, it was almost unbearable to hear people complain about getting served the wrong ice cream or having to deal with subpar customer service. Asymmetrical points of view between yourself and other can exacerbate alienation.
Also, just being around SO MUCH INTENSE SUFFERING(!) for so long is traumatic. It changes everything about how your nerves and adrenaline react to stimuli. Even a small trigger can cause you to feel so overwhelmed because your body is so used to responding to life and death situations with adrenaline. It's hard to regain a level perspective and your nerves don't know how to react to most situations.
Also also, I had seen so many cases where health insurance agencies were more interested in how to make money that how to provide compassionate care. The MOMENT somebody died, it was my job to empty their room of possessions as QUICKLY as possible so as to get a new patient in that room immediately because insurance companies don't make money on empty beds. I would hear people talk about how much money they could get from having a paralyzed patient on a ventilator because they'll be kept alive for extended periods even though there's no hope for improvement of their health. Dealing with this stuff makes you feel complicit; it makes you feel violated, like your own compassion is being used for unethical means. It makes you wonder if you're ever even doing the right thing when you exercise your compassion. It can break you.
Sorry, that's a lot to take in but it's all true. I talk about all of this to provide context and perspective. Now, how can you come back from that?
My answer is with baby steps. I find I am re-learning how to be a caring, compassionate, emotionally available person from the ground up. Acting with the level of openness and compassion you are used to right away is simply not realistic. You've got to take time with yourself to deal with these feelings and to stretch your emotions out gradually until it's no longer so draining and painful to open your heart again.
It's important to be compassionate and patient with yourself. I've had years to rebuild my sense of compassion and I STILL feel the strain sometimes. I just remember where I've come from and I remember that I'm in a learning process, or a re-learning process. I remember that it is okay to ask for help and to reach out to other people. It's also okay to fail sometimes as you make your way back.
All of that said, I'm not sure I've found a sutta that deals with this aspect specifically. Suttas have a lot to offer in terms of lessons and wisdom but it's important to be dynamic and finds ways of filling the gaps as it were. If you have an Abbott or monk you can talk to about it, do it! Someone like this with extensive practice can offer more dynamic support for something as specific as this and can offer wisdom that works in conjunction with the words you've read.
That is all for now. Thank you for your time :-)