Can a person ever fix major trust issues?

After trust is the word gamble.

I can't answer, but I can relate.

I'm kinda same as you and have in past had a hard time letting people get too close emotionally :) I've found you  don't really have to completely trust anyone else....you just have to trust yourself to be able to handle the fact that some people ( no matter how fabulous they seem in the beginning) may eventually let you down and that's okay ...cos most people are flawed. Have a full life and don't place all your happiness on any one person's actions and you'll be alright no matter what. Will still hurt :/ but it won't break you . ...Then you can just have fun, open yourself up in the moment and not worry about all that other 'what if it all goes wrong one day ' shizit.... Cos I said so :)

Made a search for trust issues, and found an interesting article. There will be several on the subject. This article pointed at four princples for enhancing trust in a close relationship.

Four general principles for enhancing trust in a close relationship:

Honesty and Integrity: Strive to be more honest and transparent in all your personal interactions. This requires taking the trouble to really know yourself and perhaps to face parts of your personality that may be unpleasant. However, this increased self-knowledge will enable you to gradually develop more trust in yourself and in your thoughts, feelings, and values. Living with integrity, according to your values and principles, makes you a person worthy of trust as well.

Nondefensiveness: Learn to be less defensive in communicating with your partner: Being nondefensive means that you have a realistic view of yourself and your partner and are open to hearing feedback. Look for the kernel of truth in any feedback or criticism you receive from your partner. You may discover that you are overly sensitive to criticism about certain subjects, yet are open to discussing other subjects. In a long-term relationship, partners learn quickly which subjects are “taboo” and stop bringing them up in their conversations. However, this is precisely the kind of censorship that leads to mistrust and tension in a relationship.

Understanding: Accept and appreciate the differences between you and your partner rather than allowing these differences to degenerate into disagreements that foster distrust. Mature love involves an appreciation and respect for the uniqueness of the other person. This means seeing your partner as a separate individual with his or her own opinions and views.

Direct Communication: Become more aware of any discrepancies between your words and actions. This type of self-awareness enables partners to develop increased trust in each other. To enhance this mutual trust, partners also need to learn how to communicate their desires and wishes more directly. When people are straightforward in asking for what they want in an intimate relationship, they feel more vulnerable and open to both loving and being loved.

Source: http://www.psychalive.org/trust-issues/

Im not sure if it will be helpful, but the principles mentioned seems being central. How to deal with them might be very personal, and different. I've previously used reading and writing around bigger matters, latest about my sexualit. All my best for you, and I'm around if needed, Hun.

anything's possible but it probably depends on what happened