Seek therapy
Besides making that personal decision to move on, you also need see a therapist. A therapist will help to identify some root causes you didn't know about and most importantly, offer a solution.
Some people are able to work through it through self-therapy but, it would be a much better idea to work with a professional who can see things from a different perspective.
Recognize your self-sabotaging patterns
People who aren't whole emotionally often don't know that they're setting themselves up for failure through self-sabotage.
Self-sabotaging, when you don't know how to receive love, can come in the form of infidelity when you're in a perfectly healthy relationship and many other problematic coping mechanisms.
There are many ways you might be rejecting love without even realizing it and you need to be aware of those patterns so you can learn how to change that.
Accept that you are worthy of love
As you do the work to identify the root causes and seek therapy, you need to remind yourself every day that you are worthy of love.
You have to fight through those lies that you've told yourself for so long for you to break free. Your loved ones genuinely care for you and when they say they love you, learn to accept that truth because they truly love you.