Late diagnosed here too. English is not my native language, and I have ASD, so if clarification is needed, please ask.
Talking to people with mental problems is hardālike, hardcore hardāeven for people without our challenges. It's like you're literally fighting a demon king with a debuff and a rusty sword. Why not play to your strengths instead? I assume you have a healthy body that can do simple manual work. There are many types of volunteer work that may suit you better and be easier for you.
Giving blood is easy and rewarding. I have been doing it for some time, and it's one of my reasons to live. One donation can save three people's lives. In Samaritan organizations, you could help with cleaning, cooking, or administrative tasks. Many of us find joy in organizing things that neurotypical (NT) people find frustrating and boring. Another option is to start with animals; many shelters need people to care for abandoned pets. Or consider working at a homeless shelter or soup kitchen. People with mental problems are much more likely to be homeless, and giving them a meal provides instant satisfaction.
Looking at your posts, you don't seem to be in the best mental space right now. The first rule of helping others is, "Make sure that there are not two people who need help," i.e., help in such a way that you won't end up needing help yourself. Drowning people tend to drag lifeguards down with them because their survival instinct makes them cling to anything for thier dear life. You might not have been in the best headspace that day to be helping others. Their emotions might have been too overwhelming and suffocated you. This is absolutely normal for late-diagnosed folks like us, as we often didn't receive help in understanding when the world is too much.
Unfortunately, as a late diagnosed autist, you need to learn for yourself where your limits are, what is too much, and how your body and mind signal that you need to slow down. I would recommend other options until you learn these boundaries to avoid hurting yourself. We were taught to ignore our limits and discomfort and push through because people do not understand autistic needs. The saying "go out of your comfort zone" does not mean that it should hurt. There is a comfort zone and a pain zone. You should never go into the pain zone. If you come home and are dead tired just want to crawl into your bed and cry yourself to sleep, you've gone beyond the pain zone. If you come home feeling a little tired but still want to make that easy cheesy quesadilla your friend gave you the recipe for and relax, you're happy with the work you did today, that's pushing beyond your comfort zone. You should NOT push beyond your comfort zone every day! Doing so shrinks the pain zone and makes it more difficult to recover. Recovery time is extremely important!
For studying human behavior: psychology and observation are key. First, learn to understand yourself. Then, understand the differences between NT (neurotypical) and ND (neurodivergent) people. By understanding yourself, you will better understand others. Have someone you can talk openly with about how they feel in the moment. For example, if you're talking and you're not sure if they are angry, you can ask, "Hey, are you angry right now, or am I misinterpreting things?" This helps tune your brain to notice patterns and get better at understanding clues. We don't notice nonverbal cues instinctively, so we need to expend mental energy on noticing, categorizing, and understanding them. The payoff is that (in my opinion) we have it down to a craft after a while. When a harder question comes and intsinct alone cannot solve it we with our patterns can solve it. Remember, taking care of yourself is the most important rule.