I think despite any advice, oneitis is something one has to experience and get over on his own. No advice really helped me for more than a day when I went through my phase. It took me about 1 year to get over it to the extent that I can somewhat look back at it and laugh. I think this is something that is universal, especially for someone going through one of their initial phase(s) of oneitis.

In a weird way, my oneitis phase is something I somewhat miss. The depression & anxiety that I went through truly broke me down in many ways. When I began building myself back up, however, I began having a very successful social life as well as sex life. I was killing it at the gym. I wanted to get back at that person and show them I was fine without them, and I would not stop until I was satisfied. I was like a mad, obsessed train. I wanted to also prove to myself that I was not dependent on anyone, which led me to constantly being in the habit of one-upping myself. Looking back at it, the melancholy and obsession I had was paradoxically motivational. I came out of it a truly better sculpted person: physically, mentally, emotionally.

I mostly learned about myself and how much I could take / handle. In my opinion, oneitis is something you will either easily fly through untouched, or it is something that drags on, sucks, and consumes your thoughts, emotions, and feelings. For most of us, it is the latter.

Those that go through it feeling the hurt & the suck come out a bigger and better man. It helps build your character and helps you realize what you thought your limits were by forcing you to surpass them. It truly forces you to become a better version of yourself.

In order to become Navy SEALS, the men have to go through the biggest suck in their life; one that probably makes any problems we have look like a joke / stupid. They are torn apart to pieces verbally, psychologically, physically, and mentally. They are then put back together, and leave knowing that they are the best version of themselves. The weak are weeded out and only the strong persevere and make it out.

Oneitis is, to an extent, similar. You go through the suck, are torn apart to pieces mentally, emotionally, and even physically. It is then up to you to build yourself back up by watching videos, reading books, socializing, helping others, etc. Once you build yourself back up, you leave a much better person than you were in the past. You also leave with great experiences to look back on later in your life if you may, perhaps, be in a similar position. Even if you find yourself in a difficult position later in life, the fact that you got through true oneitis (the nastiest form), will help you prove to yourself that you know you are good enough to overcome such obstacles.

tldr; Oneitis helps build character and will lead to you becoming a truly better version of yourself. Therefore, it is a necessary process that one must experience and go through.