Hi Alias, sorry to hear about your worries and past problems.
I think first of all you need to try to build up your self esteem which understandably has been crushed by your past relationships and experiences.
Try writing down all your good qualities, I am caring, strong, kind, attractive etc etc. You could also ask a good friend to tell you what she thinks your good qualities are if you find it difficult to think of them yourself. Look at this list every day, looking in the mirror and reading them aloud. It doesn't matter if you feel stupid at first. You have had someone tell you for 20 years that you are the opposite of these things and you need to start realising that that was rubbish. I'm sure you believed him at the time that you were fat, ugly (or whatever he said to you). You need to start to tell yourself nice things, and just as you believed him about the bad things you will start to believe these good things. Whats more, you will realise that his opinion (or anyone elses for that matter) does not matter in the slightest, what matters is what you think about yourself. If you can let yourself believe that you are attractive, caring, kind, a good friend etc you won't have to have relationships (romantic or with friends or family) where you are looking to confirm this- you will already know yourself that you are.
You can also try doing things that you know you are good at, for example if you are good at drawing, get some pens out and draw and enjoy feeling competent at these things, whatever they may be. This will also help build your self esteem and help you feel good about yourself.
The next thing I would suggest, especially in terms of your new relationship) is that you really listen to your feelings. Lots of people post on here about their partners doing such and such, is this ok or not? The only thing that matters is if you think it is ok, and the only way you can tell if you do is by listening to your feelings. If you feel hurt, sad or even if you feel numb then there is a problem that you need to address. Don't ignore your feelings, they are the true indicators of what is actually going on and will give you a much better insight than someone else's opinion or even your own reasoning. You have probably spent a long time in your abusive relationship supressing and denying your feelings. You need to learn to listen to them again.
You can do little exercises throughout the day, like stopping for a minute, closing your eyes and thinking about how you are feeling and allowing yourself to feel that. Remember to use actual 'feeling words' when you are thinking, like anxious, ashamed, guilty, elated, etc. What I mean is, for example, if you think "I feel like I don't want to be here" not wanting to be there is not a feeling, its a thought. Instead try to work out what you are feeling that is making you not want to be there, for example "I feel bored and a little impatient in this meeting. That's why I don't want to be here." Then let yourself feel what it is like to feel bored. Explore the feeling, what is it doing to you physically? Is your head hanging, are your fingers drumming, are your eyes out of focus?
The more you listen, recognise, understand and allow yourself to feel these feelings the better handle you will have on all situations in your life, not just your romantic relationships. You will learn to trust yourself and if you think something wrong, you will know that something is wrong because of how you are feeling and then you can take the necessary steps to address it.
For example, you say you are afraid of letting yourself trust your new partner. How do you feel when you are with him? How do you feel when you argue? How do you feel when he is nice to you? You will know when something is 'not right'. And if it isn't then you can talk to him about it, try to sort it out, or you can leave at any time. Because you don't need him to feel good about yourself. You are the only person that needs to feel good about yourself.
So to get you started, you are not pathetic, as you said in your post. You are asking for help with something that you think is a problem. So you can put "self aware, perceptive, strong and insightful" on your list of good qualities. Go and tell yourself you are these things in front of a mirror and believe them!
Best of luck xxx