Augh, you're not alone, Fin - although mine is not due to losing myself in another's interests. I just don't have any.
The best I can come up with is hiking. That's something I love to do - I'm alone with my dog in nature. I pass people on the trails and there's a sense of loose camaraderie without much involvement.
I've tried education, drawing classes, photography, volunteerism, crochet, writing classes (both in school and local groups). Nothing sticks.
I used to refer to myself as feeling like a "generic brand product" because I'm so...bland. I have mild, vague interestes, but I have no passion. This is not something I've been able to pretend, force, or create. I always hate when surveys ask about interests and want little bios...I indicate what I give to, what I sort of loosely belong to. But there is nothing that grabs me, holds me. Nothing I lose myself in and get in that magical thing called "flow". I tinker and wander...and while I wander and tinker, my life is passing me by.
Sort of a depressing post, I suppose, but this is an issue that's come up for me lately and I need to start addressing it. I think part of it is a safety thing - don't commit or invest in anything... hmm....I think I want to look at this more.
-Dylan