Chastity and orgasm denial discussion

Hi all. I’m no stranger to chastity, yet introducing kink into a vanilla partnership is new territory for me. I’m dating a vanilla woman who fits with me in almost every way except physically. The big hurdle is that my endurance runs far higher than hers, and she feels guilty because I don’t always finish during intercourse. Naturally, I’d love to tell her it’s by choice. I want to confess that long before we met, whenever I wasn’t seeing someone, I would lock myself in a chastity cage and deny myself orgasms. The other day I mentioned that I prefer giving pleasure over receiving it. She seemed to accept this, though there was a touch of disbelief, as if she thought I was just being polite. How can I make the leap and share my deepest desires? I know this is probably an unanswerable question. The web is full of sites offering similar advice: “talk to her, drop hints, incorporate it into your fun.” But when a woman avoids discussing sex or only talks about it for a few minutes before shifting topics, how do you capture and keep her attention?