Let's start with what's actually happening
New relationship energy is real. So is new relationship confusion about what your body wants. When you're intimate with someone for the first time in years, or the first time ever with this person, your nervous system is running a completely different script than it did with your ex. That's not a flaw. It's neurology.
Your arousal pattern shifts. Your response time changes. What felt good before might feel too intense or weirdly numb now. This is one of the parts people rarely talk about when they talk about starting fresh.