This is a tough situation for you, for your partner, and for the third person you got involved with. Everyone is distressed. I'm a relationship counselor so hear about this kind of situation fairly often. Nevertheless I would say every situation is unique, because you, your partner and the other person, are each unique.
Just that last part of what you said, about you taking home drinks and trying/hoping for a better situation, for her not to be angry, then kicking the furniture so hard you hurt yourself, when it didn't work out as you hoped, is worth you looking at. This doesn't sound like you are being realistic about the situation. But it also sounds like you feel very dependent on your partner, despite having done something that was likely to harm your relationship.
You do clearly need help and support, and I hope that you can find some, posting here has had mixed results, but hopefully has helped you understand the way quite a lot of people judge these situations. It may be unfair, but it's pretty common. Mostly in situations like this, the only way back, if there is one, is a long road of sincere work on yourself, without making demands on the other person, but with determination to change in the way you can handle relationships.
Hoping to be at ease and talk things through without anger, tears and distress at this very early stage of your partner learning all this occurred is unrealistic. Because you have already got overwhelmed by the difficulty of this and had to go to A and E, I don't advise the 2 of you to even try talking things through on your own, but to get help and support if you can, to talk together, if this is what your partner wants to do.
I hope you as an individual will get support, and some therapy, to help you sort out all this that is going on for you, and feel better. That's a really important goal, I would think, as it will likely be hard for your partner to support you at this time. I hope both she and you have means to get help, in the short term, and that longer term you can work more on what's happening for you, now and in the past, to create this situation.