Hey John, first of all, I just want to thank you for writing this out and sharing. I appreciate your vulnerability and I can hear through you words that you have a huge heart and have been through some really painful, really traumatic experiences. You don't and never have deserved that. I wish I could take that pain away, but since I can't do that, I at least want you to know that you're not alone and it makes absolute sense for you to feel this way based on these experiences. I have a few thoughts, if you're open to hearing them.
First of all, I'm sickened by what happened with your fiance; what a dreadful and disturbing experience (I don't know if there's a word that exists that could accurately describe this level of duplicity). I would have a hell of a lot of trouble after dating like something like that myself-- I mean, this is a person you literally grew up with, who shaped your worldview and your views on love and sex and self and companionship. That kind of betrayal is so much deeper than just a "bad dumping" story. I have to say, I know this may sound weird, but I get the sense that you have actually listened quite a bit to your body and your own feelings and comfort levels (aka been able to establish appropriate boundaries) following that experience, which is a testament to your character and will and your body's innately beautiful ability to heal and care for itself in the best way it knows how.
As for the sexual experience you described, it sounds like you were raped, plain and simple. Which is another compounding trauma that would reinforce for almost any human being general hesitancy at the *very* least, or almost certainly some further trauma around intimacy and partnership. That is a lot to have to deal with and heal from, and I know it sounds cheesy but I hope that you do everything in your power to be gentle with yourself. Soooo much easier said than done when you live with trauma as I know from my own personal experience (it has taken me many years and a lot of practice to flex the muscles in my brain/heart that tell me anything other than a constant barrage of "you're a piece of shit," but it does get better over time, I swear), but that's the kind of care you deserve at the very least from yourself, if you can't get that right now from other people.
As for some of the other experiences you've described, I'd like to just validate for a moment that women are some of the worst perpetrators of patriarchy; having been on Tinder for a long time looking for womxn, I recall a disgusting number of women with lines such as "men under 5'8" need not apply" and other similarly vile nonsense. There is constant pressure to meet absurd standards of toxic masculinity, and most women, despite themselves being victims of toxic masculinity in a patriarchal society, tend to think little to nothing of how their own behaviors and preferences actually reinforce this systemic violence in a very cyclical way. So I am not surprised by what you described, though I am disappointed. It's virtually impossible for that not to have a deep affect on one's psyche and general sense of self.
Frankly, I had plenty of moments when I felt like I was dating almost anyone who would give me the time of day where I feel deep existential despair because I didn't want to be alone, but I couldn't even bear the company of so many of the people I was dating. The actual viable options that I had I would say were pretty low; I was accepting some connections and relationships that were extremely vapid and conditional and generally made me feel like shit--but it was "fine" because at the time I still believed I was shit. Every person I met was reinforcing something I believed strongly about myself, and in retrospect I think I was in a sense attracting these connections to validate an idea about myself being fundamentally unlovable.
Weirdly enough, it was only once I completely called off dating (after many extremely violating experiences) and had one of my worst breakdowns at the beginning of COVID last year (I was so suicidal and really didn't think I would survive the pandemic) that I met my partner, who is the first person in my life that I've ever really felt could give me the kind of love that I always wanted but genuinely never thought could possibly exist.
I'm not wired for nonmonogamy either, and I think you knowing that about yourself is absolutely not something you need to apologize for. As a matter of fact, it's a beautiful thing for you to know on some level what you need--that is part of how you attract that to yourself. And I want to be careful with that terminology because I don't condone spiritual bypassing sentiments that blame everyone for what they're victimized for (aka "you haven't met the person for you because you didn't manifest them!" or some shit like that).
But I do want to just reinforce here that you deserve love. You deserve companionship, you deserve affection, and you deserve a family. You have every right to be angry, to be scared, to grieve. But I implore you not to give up. I am a somewhat psychic person and all I can tell you is that you will have this love. I can't tell you how or when or what exactly that will look like, but I can tell you that this period of darkness and loneliness that has felt like an eternity will end for you. You just have to keep hanging on, and even when it feels counterintuitive, keep practicing giving yourself the kind of love you wish you were receiving from another person. This will bring you immense healing, even if it feels phony or stupid or useless right now. Speak to yourself gently, treat your body with love and care, give yourself compliments and practice being present in your body. And if you don't want to do any of that shit either lmao you don't have to--you just have to keep honing the intuition that you clearly are already predisposed to to ensure that you know physically, emotionally and spiritually that you belong.
I have lived through some abusive and traumatic situations, including earlier in my life, and I know that some traumas can feel intractable. But life is so unexpected, and things can change so quickly. Please know you are not alone. Please know that regardless of what you look like, how much money you have or how much you appear to "fit in" with a society that is overwhelmingly cruel and homogeneous that you are a light; you are a unique, loving and thoughtful person with a lot to offer and a lot of love to give and receive. That's important. The world needs that. I'm sending you lots of healing and loving energy and I hope that the weight of loneliness begins to ease off your back so that you can live with the levity that you deserve. I hope this helps.