For me, the second guessing and always being on guard was/is a way to try to control the situation. I thought being in control would help me avoid future hurts and pains, but when I was always on guard, I was always stressed which puts me less in control and more in reactionary mode. I was also more likely to trust the things I was most familiar with - which meant that I repeatedly exposed myself to people who behaved abusively/disrespectfully, which confirmed that I needed to be always on guard. I distrusted people who weren't dysfunctional and lacking in trauma because I had absolutely no reference points for that kind of behaviour and I distrust(ed) that most of all.
What's made a big difference for me is learning to trust and respect myself, which, frankly, wasn't/isn't at all easy for me. I had to learn to trust my instincts, to trust my boundaries, to defend and enforce them, to endeavour to meet my own needs, to be willing to cut people off when their love hurt, to believe in my ability to handle whatever comes because I've already handled more than I thought I could, to be okay with imperfections and inconsistencies if/when they don't cause damage, to not try to control everything. I guess for me this is even more important than trusting other people but at the same time it's part of it - I trust people not to hurt me (to a certain extent), but I trust that if they do, I'll walk or run or kill if I need to. When I was a kid, I didn't have those options. I had no power and for a long time afterward, I still felt powerless. Knowing that I get to choose who gets to be in my life and on what terms makes me feel empowered.
I have similar negative associations around love but now I think of love as just a feeling, that's all. It doesn't matter that someone loves me or that I love someone, what matters is how they love me - that they respect me and my boundaries, that they behave in a way that feels like love to me. And it's okay not to love someone, or not to be comfortable with love but to just really, really like someone.