I hopefully do not come off as too ranty but its pretty important to me to post this in a way that it makes sense contextually. First i will describe the situation and than my personal situation

Basically best friends high school sweet heart after years of going out with him decided she wants her AFBB. The whole relationship she flirted with other guys (including me) and cheated on him. They broke up months ago, and she still lives in his parents house with his parents working for the summer, and he still treats her extremely well and nice. Meanwhile right now me and him are eating dinner in the house they will be using for school, and she is spending the afternoon/evening sleeping with dude.

I crushed on this girl hard for a long time (yes stupid and immature to crush on a buddies girlfriend that hard but i was a weak pathetic desperate virgin), and she flirted back and some stuff did happen, but eventually i turned into pure Beta orbier level sending her super nice messages and stuff, telling her how good of a friend she was and shit. This was also the lowest i have ever been in my life, in pure depression, doing nothing and having suicidal. Anyway i bounced back from that pretty decently, moved away, got a decent job working outside, started trying to internalize alot of red pill philosophy, tried to live by "to conquer ones self is to conquer all". I even cut off any contact with the oneitis till i thought i had beat it, but as im finding out now i havent. Tried hard to maintain frame, but she threw out way more skilled shit tests than i had responses. "you would date me if you could" etc. It has been a great lesson in humility, and how far i have to go.

Im sitting here, practicing breathing into my balls, telling myself that i am better than everyone else (useful dark triad 'hack' i saw earlier), doing anything to calm my mental state and to keep on a path of improvement and development, but i was shattered pretty hard by this.

EDIT: Should just say that part of the blow is from the fact that i spent months trying to improve, especially internally, conquer depression etc, and than have it shattered in such a short time frame. Another is the idea of leaving behind things ive relied on for so long, its another iteration of the how much further i have to go.

EDIT 2: if anyone has any advice on the best way to actually do this, deal with the guilt etc. I would be more than willing to listen and take it into consideration.