My SO and I have amazing sex pretty damn consistently, and I want to introduce another girl into the fun.

The problem is that in the past when I brought it up, she accused me of just wanting to fuck other girls and her be ok with it, so that kind of killed it for me even though I told her that she could pick the girl herself and I'd be open to another guy joining, I mean it's only fair.

She is also pretty strongly against the gay stuff, even though she's been eaten out by a girl (a dike, but that still counts imo) and she's said that she'd let a girl eat her out again but only if she's really pretty.

So I've been thinking that it is a possibility for sure, I just have to get past her insecurity/shit tests. How could I try to get her to warm up more to the idea? I know I can't FORCE her to be ok with it, but I feel I should try.