It's a vulnerability, yes; a place where anyone who wishes to hurt me could try and attack.
I always think of weaknesses, though, as being things that you can try and work on, try and fix. I don't see myself as "fixing" my attachment to Darkside.
I know that if he were to irrevokably go away -- if he were to die tomorrow -- I would survive. It's so much not like Shawn. Shawn's near-death took a lot out of me; I don't think I would have done at all well if Shawn had managed to get killed while under my care.
That's the distinction, I think. Darkside's not "under my care". I'm not responsible for him, nor is he responsible for me. He trusts that I'll be responsible for myself, and I know he's responsible for himself. Not that he doesn't take care of me when he sees something that he could do for me; I do the same for him, if I see something that I could help with... but we're adults. We don't need each other for base-level survival.
Mind-level survival, on the other hand...
Leaving aside any questionable forms of mystical connection, which are only open to debate if you're not involved enough to Know whether they're there or not, he and I are both very lonely when we don't have someone close that we can talk to on a regular basis and confide in. Wonderful as it is, LJ does not fill that need. Conversing with several people on LJ does fill that need, or come closer to filling it, but as they and I have differing schedules and differing IRL locations, this is suboptimal. Both Darkside and I need real-life friends who are emotionally and physically close.
I always have a friend like this. I always have someone I'm in love with. Darkside is a good combination of the two, and is one of the safest people I could love: he'd never harm me. Never.
I've been in love with somebody, constantly, since I was 5 or 6. That's when I started husband-hunting. I started out with kid-crushes, moved up to Unrequited Love on the Completely Disinterested, progressed to Unrequited Love on the Really Bad Friends to Have, with the occasional Unrequited Love for Good Friends Who Really Think Of You As An Amusing Kid Sister, then moved on to Requited Love for Someone Who Should Stay As Far Away As Possible From You If You Know What's Good For You. Unrequited Love for a Best Friend Who Would Never Do You Harm is an excellent choice, given that history. Especially good, given that Unrequited Love on Really Bad Friends to Have can turn so quickly to Requited Lust... may I present Shawnyel? Idiots.
I'm not worried about how deeply in love with him I am. This is a normal level of intensity for me. I would be worried about me if I were unable to be head-over-heels in love with someone.
I actually think of my feelings for Darkside as a pretty good patch on what has in the past been a terrible weakness. By loving him, and trusting him as I do, I am not free to fall head-over-heels for someone who will take advantage of my adoration. Furthermore, he watches my back, just as I guard him...
So no. I don't consider that a weakness.