You're not being paranoid you're being a doormat. Without bounds, rules, and restrictions a relationship isn't a relationship. Trust is great and all but if your partner is doing shit that actively makes you suspect cheating then you need to confront her and tell her it needs to stop or you're through. She's intentionally hiding things while gaslighting you, and she's only doing it because she knows she can. If she doesn't respect your relationship then you don't actually have one. If she wants you to be in an open relationship she needs to be upfront about it so you can decide for yourself if that's ok with you. If it's not, then bounce, because she's keeping these flirty fucks around because she's entertaining the idea of a relationship with them and keeping her options open. She's made you an option.