I never did think about making a suicide note about people to find.
I believe you should write what you think is the most important to you, if you said you felt that you didn't connect with your girlfriend emotionally, you probably mean that you wished you'd have spend more time with her or talked to her, if you do end up writting one, specify it in a way where she understands that you loved her and you regret you didn't have more time with her.
As for the parent , I too have a mother who denies everything and a missing father, you can't really reason with these types of people, they deny everything and anything. If I'd make one I wouldn't mention them, don't give them what they want, don't give them the attention and power over you, mention how much you loved your girlfriend and how much the people who mattered in your life pushed you forward, name them individually and just "forget" to type out your mothers name. I know it's a bit petty but if you went through what I went, you probably understand it perfectly, a person like that shouldn't be celebrated, a person who despises their child and uses them as a means to an end, a disgusting piece of shit like that doesn't deserve pitty.
(This was an example, not what you should write, I would personally write it like this , at least the mother part is accurate since I know how mine is. For my best friends, I don't have a lover, I'm not sure, it would require more thinking)
So goodbyes can be both happy , bittersweet and angry, you are a human, not a robot, you won't be there to experience it but if you leave, leave life without any regrets left behind, even if they don't matter after you left.