I was mocked for being upset about a bad call
Sometimes in life and in this job you are going to encounter people who are going to upset you. Sometimes they may be mean, uncaring, discontent, vindictive, malicious, back stabbing, liars, biased, arrogant, mocking, etc.
In life your feelings are going to get hurt. People are going to disagree with you. You will face adversity many times.
It is how you deal with that adversity that makes you who you are. Perhaps you will need to experience more in life to learn these lessons, but you may need to consider the field you are in. You may also need to grow some thicker skin, gain some self confidence, and you may need to get a new girlfriend.
I am sure that you are a decent EMT. In our field especially, to address your topic, we often times encounter more adversity than say a banker, cook, or any other "normal" career you can think of. Whether that be in making life-and-death decisions, dealing with violent people and situations, seeing other people at their worst moments and experiencing their emotional struggles through them, working long hours, and just seeing disturbing things such as mangled and mutilated bodies at times (obviously there are many other variable stressors.) In that, it is important to have the proper mindset and ability to handle difficult mental and physical stressors. Both personally and professionally we must be able to maturely and decisively act to make the best decisions for ourselves, our immediate team, and our patients. Some times you have to suck it up, for lack of a better term, and move on. You can't let the small things get to you because a mountain of straws will break the camel's back. Admittedly, when I was an urban 911 basic years ago I do not recall ever being the sole provider responsible for making life and death decisions; although, that is not to say that it does not happen to others.
Additionally, this is a field in which a stable support structure outside of the workplace needs to be suitable and healthy to deal with our stressors. Our field is rife with substance abuse, sleep disorders, divorce, and PTSD among our colleagues. Family is supposed to be supportive of you. Friends are supposed to be supportive of you. We as the "helpers" sometimes - as tough as we might be - need a little helping of our own. Personally, my girl is an RN. It is nice to be involved with someone who understands exactly what I'm talking about and shares the same mindset as I do, and also who experiences the same stressors that I do. It is a stable support structure. My ex, not so much... It was not helpful to say the least, so I have seen both sides of that coin, so to speak. You can also talk to your co-workers or supervisors if you are having a difficult time as it relates to the job.
However, if your loved ones are toxic to your aspirations and goals, then you may need to cut them out of your life. Some folks may be harder to cut out than others, and often times there are steps and attempts to reconcile that should be taken before shutting them out. Your "girlfriend" sounds toxic. I would not be with anyone who called me a fat loser who can't save people (or similar.) Not that I would be offended, because, well ---- her... is what I'd say. I would remove myself from that persons obvious path of self-detriment. Not to mention the fact that she is listening to the scanner at home and then making violent outbursts related to the type of call you were on. Both of those factoids indicate level 9 out of 10 crazy (aka RUN! crazy.)
In summary, and I apologize in being so long winded, you need to come to terms with the fact that life is tough, and you're going to get hurt feelings and feel like a failure once or twice. Don't take things so personally even if they are personal. You've got to be tough and get up, brush it off, and continue moving forward towards your goals. The only place where success comes before work is in the dictionary. And trust me, life can be hard work. Turn the other cheek on this girl of yours and find someone who appreciates you. The search may be long, but I promise that in the end you will be happier alone than with someone who treats you with such disrespect.