I agree completely with what GalaGirl and XTremeMeow wrote. Run from both of these people, for your own physical and emotional safety! Please don't let yourself be gaslighted: What you experienced was indeed sexual violation by Chloe and betrayal by your partner.
I hope that you will soon be...
I agree completely, Tinwen.
It seems to me that the issue here for you is not polyamory vs. monoamory, but rather not having enough time with your partner. It makes complete sense to me for you to worry that if your partner were to have another partner, you would have even less time with him...
Being "good" at dating, like being good at anything else, takes practice. I hope that you will come to see yourself as worth spending time with. Others will then see you the same way (and might very well see you that way even before you do).
Welcome! You don't have to have dated to get to know others -- you just have to meet them and get to know them. What scares you about trying other relationships, now that your partner has stopped thwarting you?