Listen, I can say from reading all this almost of all of your problems stem from a lack of self-worth, which is rooted in the ego. You should read a book called A New Earth.
Your lack of self-worth stems from comparing yourself to others, and not realizing you are fine the way you are. Your lady's desire for big penises (unless of course she has an abnormally large vagina), and the tiniest percentile for size, is also rooted in her ego. She is basing her partners worth on superficial things, and attaching them to her own sense of self. That is why she wants the big penis.
Her ego wants to feel good. Her sense of ego wants to feel like it is attractive and special, and she gets that through attaching herself to the man she is with, and she is judging her man's worth by the size of his dick.
Why? well, that's how she has been influenced, (You have to realize with all this advertising about Size Matters, and Sex and the City, and girls gossipping about how all their boyfriends had 20 inch dicks and outright lying because it makes them feel like hot shit in front of their friends, she has had a lot of negative influences) and remember, people believe wrong things on mass levels, no matter how stupid an idea is people will take it to be the truth if there are enough people going along with it. The vagina only requires about 4 inches to stimulate the sensitive part at the entrance of the vagina (of course there are girls who want cervical stimulation but that is not a requirement and the reality is the reason most women do not experience orgasm during sex is because women are influenced throughout their whole lives to feel that sex is wrong, and sex is bad and that they should not enjoy sex)
It's like, my last girlfriend, she used to hold my dick in her hands and put her hands down my pants all the time and just want to hold my dick allll the time for no reason, not even to jack me off, and she'd grin at me like she was really proud, and I didn't understand it. She'd just hold it like a trophy. Why? because she is attaching her sense of self worth to size of her boyfriend's dick.
There is a lot of media and bullshit being passed around that is trying to spread the idea that a man's worth, attractiveness, and so on are based on the size of his dick. So by having a big dick, I am making my girlfriend feel more confident about herself, and pretty much making her feel like hot shit. Now, this girl was petite, she stood 5 foot 2 and we never had sex because she would get extremely needy when it came time for sex (she had a lot of self-esteem issues she would hide from me) and that would turn me off so bad that I'd lose all desire to have sex. But needless to say, a girl that size does not need a guy with a 6 inch girth and I don't even think it would have been comfortable for her if we had gone through with it.
But again, the Ego, because I would turn her down, she'd feel as if she was not attractive enough to please me, she'd always try to get me off because by doing so, she would have confirmation that she was attractive enough to make me (an attractive man in her mind) cum, thereby elevating her sense of self worth. And again, i'd always turn her down when she wanted to give me blowjobs, I can't say why, well I will say it had to do with A) the crazy pleased look she'd get on her face when she started getting me off, like she was satisfied with herself, and it was like I could feel that it wasn't necessarily that she wanted to make me feel good, but because she wanted to make herself feel good about herself by making me cum. and B) I didn't have much libido when I was with her because I had recently stopped taking Zoloft at the time which pretty much made me never want to do anything.
Now, regardless of whether she has been influenced by these things and she is not directly responsible for her incorrect beliefs, she is still a bad person for you to be with. And the reality is that the only reason you want to be with her or ever wanted to be with her was because you didn't believe you were good enough inside. That is why you didn't walk away when you should've, and that is why you'd hang on so tightly instead of dating a more attractive, smart, caring woman and having a proper relationship that you deserve. Everybody deserves a good relationship, but you need to work on yourself first. You need to start liking yourself, and understanding a lot of the myths in culture today. Aside from that, women are not attracted to needy man, hell, i'm not even attracted to needy girls. Needyness and jealousy is created from feeling like you're not good enough, because you fear that somebody is better than you and is going to swoop up and take who you think belongs to you. So working on your own self-esteem, and not ego, self-esteem comes from inside, it's not based on the size of your dick, how nice your car is, how smart your iq test says you are, or how many girls you've fucked or anything external. And it is something you can develop.
So I will reccommend you a few books.
A New Earth by Eckhart Tolle
Think and Grow Rich by Napoleon Hill
and i'd recommend you some more but those are very powerful and will really help you so, that's all I can recommend for now, because I can't think of any haha.
Anyways, assah lama laykum brother, just kidding but seriously, take care of yourself, and I hope to hear back from you. Be strong.