The work of this starts by confronting your past. It's helped made you who you are, but it's by no means who you always have to be. Talking about the things you've been through (with friends, family, or a therapist) will help you make sense of the patterns -- and company -- you keep.
Meditate on exactly what it is you want in a partner, no matter how casual. A baseline is always a good reference point to have, even if it's as simple as saying you'd like to occasionally see them during daylight hours, hear back from them in a timely manner, and be treated with the same amount of respect you'd expect from your friends. If your baseline needs aren't being met, stop seeing this person.
And let go of being too analytical and judgmental. Feeling gun-shy after getting out of a tough relationship is normal. But assuming everyone is going to cheat, lie, and hurt you? Just impractical… especially if you're staying away from those red flags we discussed.
Eventually, I realized holding everything in was more work than it was worth. Shedding my misgivings, and relearning how to be vulnerable, was the most empowering thing of all.