How do I better myself and not always think the worst or that someone is up to something?
Thank you very much for your question. Let me say that I am really sorry that you are going through this hard time. I agree with you in seeing this particular situation not only as something to improve regarding your relationship but also as something to do with yourself, so you can be way happier. I really appreciate these words of yours.
First of all, it's important to say that, normally, when we have trust issues we have a lack of confidence in ourselves, and that's why we think that the other one could betray us always as we don't feel good enough. Also, that lack of confidence comes from a lack of love for ourselves, and the people that we are (our self - esteem). 'As I don't like myself that much, I don't have big confidence in the person that I am.'
Due to that, I would recommend trying to improve your self - esteem by doing some important things:
1. Observe your life in its main contexts (family, work / studies, couple, social, personal) and see where you are behaving in a way you don't like and why. Try to change that.
2. Try to communicate yourself in an assertive way, respecting your point of view while respecting others' points of view (sometimes we tend to be passive, aggressive or passive-aggressive and it's got an impact on our self - esteem).
3. Try to treat yourself properly and assess the steps that you take in your life in a fair and non-judgmental way. Try to accept that you are not perfect and that's fine.
4. Try to improve the relationship that you have with yourself by doing things that you really enjoy and that are meaningful for you.
Some psychological approaches of ACT, Mindfulness, CBT and Positive Psychology could be very beneficial for this situation.
I honestly hope it goes well and I am sure you will be able to achieve all your purposes. Remember that, in the end, you only need to love yourself better to be able to be happier and love others without problems. Wish you the best. Best Regards.