@azumeow
I'm not too good of an advice-giver if it comes to relationships, but dealing with aggression or hate, negative thoughts all in all, is (was) a big part of my life.
(correct me if i understood something wrong, you are pissed at the girl?)
Many years ago, when i was, like, 9 or so, i was a pretty darn aggressive folk, always looking for trouble in any way. But to this date, it has been about 10 years without any sign of negative thoughts, aggression or anything like that.
10 years now am i living a pacifist life, and it really is something worth trying out.
And now to the question you would be asking: How? How can you just not hurt anyone (be it physically or mentally(hope its the right word here)) or how can you just not feel hate or negative things?
To the second part: Feeling hurt, hating something/somebody or feeling negative things in general is the most normal thing in the world. It's about not being bothered by these feelings. Just pushing them aside is a bad way to approach them i experienced. What worked for me was finding my peace with them.
Example: Oh, a good friend of over 3 years suddenly decides he doesnt want to spend time with me anymore and doesnt want to tell me why? Instead of just saying "fuck it, i'll just forget that" say "Im fine with that. It is his decision and there is no way for me to change that."
This helped me to feel better on any occasion, sitting down after a bad/negative experience and just thinking about it until i can find my peace with it. Meditating, in other words.
To the first part: It's easy, just avoid to hurt people. Even if they deserve it, i would feel guilty if i hurt anyone. [might not be best, but i like it and like living like this]
So to sum it up: Meditating and making peace witht he world has helped me being calm as hell and being admired for that by all my friends. If they have a dispute, im the first one they ask for help ^_^
[While finishing this text i started asking myself if it makes sense or even helps anybody, i always do that so if you see anything that doesnt make sense in terms of context or anything please tell me

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Lockhart wrote:My favorite buddhist monk Ajahn Brahm (lots of his talks on YT, check it out if you like) often says that unhappiness is “asking from the world what it can’t give you”. The world can’t give you one and only special true love that’ll make your life complete in every possible way, but it can give you real girls from flesh and blood and bone and spinal fluid.
Exactly that, i'd like to add, it's not what life gives to you, it what you make of it.[If life gives you lemons, make lemonade]
You can't just expect everything to just come to you.
He's my favourite buddhist monk, too.. so many good, wise words C: