This is something I've been struggling with too. I love my partner, but they can't be my only source of social interaction. We each have our own lives in addition to what we share with each other.
It's been very uncomfortable, but I've been forcing myself to try to engage with people that I share hobbies with. Think about the things you like doing and then seek out those groups.
One of the advantages of trying to make friends as an adult is that, people are generally welcoming. If they aren't, it's probably not a group of people you want to spend your time with anyway.