Ruminate over it.

You continue to see Gemma, but the topic of Jeremy never comes up. She senses you're acting differently, of course, and she's smart enough to put two and two together. But it's easier just to ignore it, it seems, and to continue fucking each other's brains out. The sex is still fantastic, as usual, but it's lost something, something that you don't think you'll ever get back. You try and reason with yourself. What's there to be jealous of? After all, she's not your girlfriend. At most, she's your mistress. You're cheating on your wife with her.

But you can't stop thinking about him. You imagine him taking her out on dates, doing all the things you wished you could do with her in broad daylight, but can't. Worst of all, you imagine what she does to him. Picturing her on her knees, bent over, the dirtiest, most carnal acts of sexual depravity. If she does it with you, she's for sure doing it with him. And what if you're getting the sloppy seconds? The thought of being with her after he's cum inside her makes your skin crawl.

Your jealousy curdles into something uglier - anger. All that money you spent on her. She was just using you for sex, for gifts, for entertainment. But the anger isn’t just at her. It's at yourself. For caring. For letting her turn you into someone who feeds on the scraps of her time and attention. After a few more months, you decide it's time to settle the issue of Jeremy once and for all.