Heya Llv,
Sorry to hear about what you're going through at the moment. The heart break must've been really painful, and it's impacted your life a lot even till this day... No matter how much we want to change things in the past, or have loop thoughts on "what ifs", the reality is those events are now in the past, and there's no way of changing the past at all. The best we can do is to learn from the past, so we can improve ourselves for the future.
Getting over a heart break isn't an easy feat either, some may take just a few weeks, but some could take up to years. I hope you'll be able to be more kind to yourself, and recognize that we're all flawed human beings with our own unique traits and such. Mistakes happen, but as mentioned before, we can learn from them to better ourselves.
Everyone is responsible for their own happiness. The reason why I say this is because, if you feel the need to be responsible for other people's happiness, then that's equivalent to throwing away the life you want to live in exchange for other people's approval. It creates a codependency relationship which can be unhealthy. In a relationship, both sides are responsible for their own happiness (which creates friction and conflict when one person wants to do something/makes a point, but the other person doesn't/disagrees), At the same time, they both accept each other's weakness/flaws, while supporting each other through hard times.
Take some time off from the dating scene and work on yourself first. Find what makes you happy while discovering your strengths and accepting your weaknesses. Give yourself some self-love and see yourself as a friend. Treat yourself the way you want to treat your friends. You truly deserve a better person in your relationship, but before that person appears in your path, discover and put yourself first before anyone else. Remember that we are all responsible for our own happiness.
Hope that helps Llv, happy to hear from you more if you'd like to share more.
Jt