You offer some men perspective. But the situations you describe look different from the other side.
The woman who break up after 8 months saying "did you expect marriage?" might be cruel or might not see those 8 months as "perfect" as the man. In fact, she might have had an awful relationship where she was the one working, paying all the bills, doing all domestic chores, taking care of the boyfriend and basically getting no real appreciation. It could be a forgotten birthday even after she told you it was important to her, it could be constant complains because he wanted other food. Or maybe that he loves to play video games more than he loves spending time with her (or prioritize the video games over looking for a job). Point is, from her perspective, she has put a lot of effort in the relationship to only get pain. He has been hurting her. Now, according to the premise, if he has hurt her feelings, snapping at him would be understable, right? Except society expect women to be nice even when we are hurt. So of course she would be considered a bitch. Because from his perspective everything was great and he wanted to marry her. So what she wants become irrelevant. She should just cave and give it to him regardless of him hurting her, right? Well, no.
Your other example about "the perfect girl". I've lost count of how many times a woman says she is not interested in a man, using those exact words, yet, her rejection is ignored. The man convinces himself that "no means maybe" or that "she would change her mind if he sticks around" or that "once she really know him, she'll like you". They keep ignoring all the times that someone reminds them that she is not interested in him romantically. In fact they have had a conversation where she explicitly told him that she cares about him as a friend, but only as a friend. That she doesn't have romantic feelings for him. He would assure her that they are just friends. Yet, he expects that when she is a low point in her life, he would be there for her and that at that point she'll get in a romantic relationship with him. So finally, she is at a low, so he helps her. And when she still reject him, he throws a fit, because "she owes him" and she has been "stringing him along" (Regardless of her being a good friend to him and being clear about not wanting something romantic).
So what can you change? Learn to accept rejection, learn that many times things won't go as planned. And most important, that doesn't mean you are a failure. In fact, things don't go as planned might be the start of something better. After all, you don't know if that "imperfect" woman you'll meet latter in life. The one that is nothing at all what you imagined your girl would be is the one that would make you happy. Also learn to listen and accept what people is telling you. If someone says that only wants to be friends, chances are that they are being honest. And if being "just friends" doesn't work for you, you are allowed to be nothing.
We also experience rejections, break ups and disappointments in life. Go out with friends, vent, then take care of yourself, do nice things for yourself, start a new hobbie or do things that you enjoy (and have nothing to do with meeting the right person) and when you feel better, you can try to meet people again. Or maybe by that time you would have already meet that person while you were doing something you love.
The point is, everyone deal with their own pain. Woman are expected to do it in a quiet way. To keep it to ourselves. And blame ourselves. But everyone has the alternative to call their friends for help and make it easier. And eventually, let it go so we can move on.
