Social Etiquette Struggles

Hello everyone, I'm new here.  My name is Andy and I am actually a single man in a serious dating relationship.  The week between Christmas and new years, I stayed with my girlfriend's sister and her husband (and my girlfriend was there too).  I had a wonderful time, but after it was over, my girlfriend informed me that I was rude to her family unintentionally the whole time I was there.  I struggle a lot with social etiquette in ways most people take for granted.  Here are some examples what I struggle with:

For example,

-when my girlfriend's sister did things kind for me, I didn't say thank you (but I felt thankful in my heart)

-I’m afraid to go out of my way to help someone. They have to ask me for help first. 

-If there’s tasks needing to be done, I just stand there not knowing what to do and wait until someone tells me something specific to do.  Apparently I was expected to take the initiative to clean up around the house while I was there but I didn't know what to do so I didn't ask.

-I’m not considerate of others in my words and actions. I say things others take the wrong way or I do things that make others think I’m rude.  While I was visiting, I meant to ask if I could stay an extra day here's how it came out of my mouth: "I've decided to stay another day" which sounded like I was making a demand.

-In romantic relationships, I’m a passive man and it typically leads to a breakup. My girlfriend felt hurt by an unkind comment of her brother-in-law.  She was uncharacteristically quiet the rest of the time but I failed to take notice of it and comfort her.

-At another gathering (thanksgiving), I put a hot metal bowel from the oven on her uncle's nice wooden table without a hot pad because I wasn't paying attention.

We've been dating for five months now and I had warned her of my ADHD, but she hadn't seen it really take effect until I visited her family.  It hurt and concerns her so much that she says if I can't fix this, she'll have to break up with me because she doesn't think she'll be able to tolerate it.  I love her dearly and really do not want to break up, but I fear it's impossible to completely fix everything even if I try.  She is more of the mindset that actions speak louder than words so she can't trust me until she sees results.  This hurts me a lot because I feel it's not my fault.  She acknowledges that it's not my fault but it still bothers her and she cannot tolerate it.  Is there any way I can get past this issue and learn social etiquette as an adult?