How can I best let her know, that this incident hurt me and probably damaged our (non-romantic) relationship without her connecting me with negative emotions?
Your desired outcome is for your housemate to be aware that she has lost your trust (as per your comment elsewhere) and damaged your friendship. Let’s look at how that might go:
Besinnungslos: Housemate, you have lost my trust and damaged our
friendship
Housemate: How did I do that, besinnungslos?
Besinnungslos: by talking to your friends about that time I was
aggressive and rude
Housemate: And how do you know about that?
Besinnungslos: My door was open and I was listening
Housemate: Well, a
trustworthy friend might have let me know he was there and closed his
door. You, besinnungslos, have lost my trust and damaged our
friendship, which frankly was a bit shakey already after that whole
aggressive and rude thing you did that time.
Besinnungslos: ………..
And while that is a deliberately not a realistic ‘script’, it does contain the essential reactions which your broaching this with your housemate are likely to provoke.
The underlying issue is that this tale doesn’t begin with her talking about you to her friends, it begins with you acting in such a notable way that people are still talking about it months later. People are reacting to your behaviour, and asking them to react differently is asking them to go against their natural instinct and give you a pass. If you want them to react differently, you probably have to try to change how they think about your behaviour subsequent to that previous incident.
Obviously we don’t know enough about that to give specific advice, but here are some things to think about:
Did you and the person you were rude and aggressive towards talk
afterwards to patch things up?
Did you apologise to the target of your aggression and to everyone
who was around the incident?
Have you sat down and thought about why you reacted aggressively and
rudely to that person and how you can avoid behaving in that way
again?
Did you ever tell the others who were there that you are not proud of
what happened?
In short, did you ever do things to reassure the people who experienced that incident that you regretted it and any effect it had one them and wanted to make amends and to make sure you never did something like that again?
If you have done some or all of that then you might approach you housemate and explain that you heard part of the conversation from her private party from your room and though you really didn’t hear what they were saying, you could tell it was about that incident, perhaps something like:
I really just heard my name, you know the way that catches your
attention, and enough to know you were talking about the time I blew up
at Joe Bloggs. So I just wanted to say again how sorry I am for that.
I really surprised myself, to be honest, and I’ve thought a lot about
it since I apologised to Joe. I understand how I can avoid making the
same mistakes again and I really appreciate how you guys have been so
cool about it. And I’m really sorry I didn’t close my door sooner when
I heard you talking, I’ll be more careful about that in future.
That should be enough for her to understand that:
- You have taken that aggressive incident seriously.
- You want to avoid it happening again.
- You know others were affected and have sought to make amends.
- The fact that she was talking about it has upset you.
- You realise that eavesdropping isn’t cool.
Thereafter you can only trust to her good nature to recognise that you have not been accusatory, or tried to dictate her behaviour, but that you continue to regret the original incident and that you know eavesdropping is a jerk move.
If you hadn't, in fact, given a though to the aggressive/rude incident since it happened, don't pretend you did. Be honest and admit that:
I really just heard my name, you know the way that catches your
attention, and enough to know you were talking about the time I blew up
at Joe Bloggs. So I just wanted to say that it was a bit of a shock to realise that incident is still in people's minds. I've been thinking about it since I heard you talking and I'm going to see if Joe will accept my apology, and of course I want to make amends with all of you that were affected and work on myself to make sure I don't mess up like that again.
Essentially, in that scenario, you have to offer something to get something. You can't demand that something which made people uncomfortable is set aside and never mentioned, but what you can do is try to demonstrate that you have learned that actions have consequences for other people as well as you, and sometimes you have to make amends.
Trust breeds trust so you have to give her reason to trust you.