The experiences of our past shape who we are. They often help us determine our course of action in the future. Although we can't let bad experiences fill us with fear, preventing us from creating good, positive experiences in the future, we would be fools to not mind the lessons we've learned.
In relationships, we need to be able to approach new people, and new opportunities with an open heart. When we find that person that we truly want to be with, and who wants to be with us, we should be able to put down our defenses, and be vulnerable. We can relax in an openness of self, willing to give from our core energy, and open to accepting what they give. Past misgivings from other relationships need to be dealt with on an emotional level. The hurt given to us through life, whether it be with other interpersonal relationships, damage done by strangers, or just the inevitabilities, or random events that cause us pain, and grief, need to be dealt with on an emotional level so that we can come to terms with that hurt, end our grieving, and accept the good things that are ahead of us.
However, red flags are red flags. If that special someone starts exhibiting concerning behavior, it shouldn't go ignored. Frank, and direct conversations about it, expressing concerns, and the feelings generated by their behavior should be initiated long before those behaviors do damage. From there you will get a sense of how your partner wants to deal with it.
Do they listen to your concerns? Do they get defensive? Do they try to turn it back on you, or do they engage in a dialogue while accepting their own responsibility to your feelings? Do they apologize curtly, and try to end, or steer the discussion elsewhere? Do they continue to exhibit the same behavior afterward?
Take notes. I know that sounds formal, but keep a journal or a diary. Don't just rely on your memory, which might be clouded by emotions while engaging in such conversations. Keep notes in case you need to look back, and remind yourself how things happened, what was said, how it transpired. It will help keep you from feeling crazy if your partner is trying to gaslight you, or manipulate you.
But, you have to deal with you first. Take some long, hard, critical looks at your past. FEEL the feelings, and emotions tied up within your experiences. Get professional counseling if you think you can't resolve those past feelings. Trust me, talking out all of the jumbles of thoughts, and feelings that can sometimes overwhelm is vital, and helpful.
Most importantly, don't assume the worst of a person just because things can sometimes be difficult, or even more, just because your past has been difficult. Talk it out. Talk it out. Talk it out. Be open, be honest, especially with yourself. If your partner can't handle your honesty, your feelings, or what you want from your relationship, they're probably not the right one for you...