What field are you planning to work in once you graduate? Similarly to joining meetups focused on your hobbies, you can meet and network with like-minded people by going to meetups related to your field. I don't think it's a huge deal that you're still in school--you might connect with a great mentor and/or make inroads in your industry.

As a reader, check out local book clubs! Just about every library has them. Also, look into adult school classes. A lot of communities have community education courses for adults (for example, Chatham Adult School and SOMA Adult School) and you can meet people with similar interests by taking fun classes with them.

It's tough, I know. And it might take some time and a lot of effort to meet people who really click with you. So I say give all of those things a shot, and maybe even involve your partner in trying to be more social and meet people! Even if you go out as a couple, you might meet other couples in your demographic (and outside it...one thing about adult friendships is, age doesn't matter as much anymore. You might really hit it off with somebody who's 10 years older than you) and make "couple friends" that way, which can turn into something lovely on its own and lead to 1-1 friendships.