When we have been betrayed or abused, we start to not trust our instincts. It isn't others we don't trust, but ourselves. We think by making the choice we did, that we failed to protect ourselves. That we should have seen who and what they were before things went bad. Sometimes we want something so badly we will ignore the obvious signs and stay in a situation that just erodes our own belief in our ability to distinguish a good person from a bad person. It makes it even harder if they are borderline but have traits that are so against what you want in your life. And it is even harder when it is someone we love or so desperately want to love us.
I have been there. I still have problems thinking my gut instincts are broken but it isn't that they are broken it is that my mind gets in the way and reminds me of the past. I listen to what someone says, and I also watch what they do to see if what they say matches with what they do. Your subconscious has been trained by your past situations and it learns from those situations what it needs to do to protect you. That little jolt of fear when someone says something like "I won't hurt you" is your subconscious reminding you that this isn't the first time. It means you need to pay attention and open your eyes and use your mind, go over what has gone on and determine if this jolt of fear has a substantial basis for what is happening now. Has this person ever done anything they said they would not do? Have they told you they would do something and then not do it? Have they put you into a dangerous situation? Have they asked you to do something you don't want to do and not care about your feelings? Or have they respected those feelings and tried to understand?
In order to know what to do, you must be your own detective, become your own Sherlock Holmes and dissect every situation. Is it only his absence that has hurt you? Or has he done something else? What does he have to gain by coming back into your life? Is he seeking anything from you other than to get to know you and be part of your life in whatever capacity you are willing to allow?
You don't have to decide at this moment. Put up your shields. Let him know you are wearing your armor. If he truly cares about your feelings he will give you time to see him for who he is. If he doesn't want you to know who he is then he will push you and hide from you, and not give you the time you need. Don't be afraid to be direct and lay out your concerns. But if he has not done more than not be there when you were growing up, then it might be true what they have told you. I have a brother whose ex did not allow him to see his son. He fought for as long as he could afford to do so but going to court and still not getting anywhere is expensive. He also gave up and decided when his son is old enough he will start asking questions and eventually he knew when his son was an adult that his ex could no longer keep him from his son. His son is now an adult and they did get together and his son learned what his mother did. Eventually, the truth comes out. Maybe you are finally learning the truth. But I agree. Be cautious. If this is too much for you to handle, you have the right to ask them to back off, give you space and let you live your life. Whatever you ask of them will be a way for you to gauge whether they are true or not true. If there is a deadline, then this would be enough for me to say, 'no' and go on with my life. There can never be a deadline when helping someone heal from past trauma and pain. They heal at their own pace and they have to feel secure in doing so. If they do not offer this security then I would pass. Or at least see if they will step back and give you time to see who they really are beyond the words they tell you.
You have the right to walk away now or at any time, don't ever let someone say you don't. Decide what is more important to you and go for it. Don't worry about what others say you should do. You are the only one who knows the full story from your point of view. Lean on what you have learned and let it guide you. I wish you all the luck and love you need. 🫂