I don't know if this is the answer you're looking for, but I can give several bits of advice on what I think can help in having successful relationships:
- Be happy in yourself
If you have a happy and fulfilling life as a single person and don't allow yourself to depend on other people for your emotional wellbeing, it's easier to notice whether a relationship (romantic or not) is having a positive or negative impact on your life.
Relying on a romantic partner for your own happiness gives them a huge amount of power over you. People who can be emotionally abusive will see how much you want to sustain the relationship and use this to manipulate you.
One technique that can help at the start of a new relationship is to limit the amount of time you spend with a new partner: not only does this prolong the "honeymoon period" where the relationship is at its most exciting, but it also gives you time to reflect and evaluate the other person, and ensures that you continue to make time for your other hobbies and friends. In my experience, giving up hobbies and neglecting friends in favour of a relationship is a huge mistake.
- Know your own mind
This can be challenging at times, but when making decisions try to think "is this what I want?" If you find yourself being swayed by persuasive or dominant personalities, give yourself time to make decisions at your own pace. There's nothing wrong with answering someone's request with "I'm not sure right now, I'll get back to you on that" or "I need to think about it, I'll let you know". Anyone who continues to pressure you for decisions may be trying to manipulate you.
- Set boundaries early and be consistent
I'm not generally one for setting rules, as I believe every relationship and situation is unique and requires some flexibility. However, if you find that your behaviour is easily influenced by others, try setting boundaries from the beginning and be sure to enforce them consistently. This doesn't just apply to the physical side of a romantic relationship. If, for example, you don't like people owing you money, then don't lend to people and just say "Sorry, I don't feel comfortable people owing me money". Again, anyone who doesn't immediately respect this would be a red flag for me.
When you cross your own boundaries once, it is much harder to enforce them again as the other person will use the 'but you did this before, why wouldn't you do it again?' argument, which is difficult to defend.
- Trust your friends and family
If you have a good circle of friends and/or close family that your trust, use them as a sounding board to validate your thoughts if you believe someone is being abusive or taking advantage of you. Don't trust someone in a new relationship above your established friends, or it enables them to manipulate you by telling you that your friends/family are wrong and you should only trust them instead.
I hope this helps. They are all things I've learned to do as a result of previous relationships because I am a naturally trusting person too, and it's easy to believe the best in people and end up getting hurt.