4. He wants to win you back. Sex conjures all sorts of powerful feelings, and it's impossible to be immune to them. Even hugging—let alone naked full body groping—produces the bonding hormone oxytocin, which can make you feel loving and cuddly towards someone you don’t want in your life anymore. And that's his plan. The only way to make sure you're not fooled by your body is to stay away from ex sex.
5. He wants a friend with benefits. Ah the old friends-with-benefits conundrum. Here's the truth: You can't have a casual sexual relationship with your ex, and sex is the least casual of all relationships. There are very few benefits here, and a lot more drawbacks: It'll hold you back from entering a new relationship; it might even prevent you from dating people, because you'll still feel like you have a boyfriend—but not the one you want.
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6. He misses you. Aw, that's sweet. But not a good reason to have sex. Missing someone is normal—it's part of the grieving and recovery process, and if you have sex, both of you will have to start that process all over again.