Been Struggling with Open Relationship After Divorce

So I got divorced last month and now I'm in an open relationship. It's been... complicated. I've always been one to keep things strictly monogamous, but after the divorce, my ex said we needed space, which kind of threw me into this new world where there are no rules except what you make yourself. And honestly, it’s a lot. I mean, today was rough. My partner, let's call her Anna, suggested we try something new at our place last night. She wanted to do a foursome with two friends of hers who she set up for me beforehand. We agreed and went home. But the thing is, while it started off good, I found myself craving more than just physical stimulation from any of them. When one guy was inside me, I kept thinking about how much more intimate it would feel if he had a closer bond with us. The night ended up being a bit of a blur, there was so much happening that I couldn't keep track. But the morning after, lying in bed alone, I felt this overwhelming sense of emptiness. It's like I'm not getting what I need from these interactions. Sure, there’s pleasure, but it doesn’t feel fulfilling anymore. So here’s my question to you all: Is it just me? Am I missing something, or is this normal for someone in an open relationship after a divorce? Should I be looking at monogamy again or am I okay where I am and just need more time to adjust?