I think envy and jealousy may keep you from seeing the whole picture. You want something that others have, and you compare yourself negatively to them because you don't have what they do.
People tend to find others attractive because of what they have. They don't seek someone who is lacking in order to give them what they don't have. The most amorous attention I've gotten has been when I've felt the best about myself and been confident. There are also some who are attracted to such things because they want to feed from it or diminish it, so it's not a guarantee that mutual attraction is going to lead to mutual fulfillment, but it's easier to recover from such things if one is confident in who they are and likes themselves.
Imagine a guy being attracted to you who feels like crap about himself and wants you to help him find his identity. It's an instant drain. And you can't help him find what he can't find for himself. So you may get frustrated and leave him, which is self-preserving, or you become co-dependent and spend all your resources trying to build him up, but it won't work because he doesn't have the necessary foundation, and he ends up resenting you for not fixing him and you resent him for not being fixable. Now turn that around to you being the one in need, and you can maybe see how it's likely to end up with you feeling even worse than when you started.
Back to the jealousy and envy. I would suggest studying the people who have what you want. Ask them questions about what their relationships are really like, and if they feel as fulfilled as you imagine they do. Ask them what they give up as well as what they get to have those things. Ask them how they feel about themselves - are they as confident as they appear? Are they truly satisfied, or do they also long for things they don't have? Do they feel like they have a firm grip on being an adult, on being successful, on being in a relationship, or do they also struggle, doubt, and feel inadequate? If they are confident and fulfilled, why? If they were to lose their relationship or their job, would they have the internal and external support to manage?
I think it's great that you asked guys out. Yes, you got rejected, but you can use that as a learning experience before trying again. What did you observe about them, about you? What were their responses, and were the responses reflective of you or of them? If they were reflective of you, what can you learn from it that helps you to improve your strategies ather than feel diminished? If it was about them, what does that reveal about what you would do best to avoid in future romantic interests?
A final thought. I recall when I was in my teens and early twenties, I said horrible things about myself and hated myself. Enough people pointed it out to me that I decided to change it. I started to like the things about myself that were different from others, and I praised myself rather than condemning myself. My attitude toward myself shifted, I began to enjoy who I am, and others were happier to be around me. I embraced my weirdness and many people seemed to enjoy it because I enjoyed it, and if I was in a relationship that drained me, with someone who didn't appreciate me, I was better able to recover because I had created a foundation of self-acceptance and self-worth. If someone knocked me down for liking myself, it was a reflection of their lack, not a reflection of me. Someone who knocks others down needs that power because they feel weak and use the experiences to make themselves feel stronger and validated - those are people to stay away from. If you learn to like yourself, especially as you can't be anyone but yourself anyway, then you will be attracted to yourself, and others will naturally follow suit without you having to try. It may seem like this is a huge task to undertake, but it's not a task when you're enjoying liking yourself and getting benefits from it. When it's focused on earning something from others, then it is indeed a task, and the goal is external and outside of your control. If you don't enjoy being yourself, being in a relationship with someone else won't change that, and in fact may make you even more insecure because you're striving to meet an invisible bar set by someone else rather than yourself.
