I probably shouldn't answer this, as I'm fairly pessimisic about them anymore, but here's my take on what normally happens with mine.
I meet someone, and he finds my quirks endearing. I am oblivious to this for a while, then notice he's become extremely protective of me. That is my cue that he's interested. If I'm amenable to something happening between us, I don't avoid him and let him do his thing to get it started. It progresses from that point to extremely long conversations about our backgrounds, lives, hopes, etc. The learning about each other stage lasts anywhere from a few weeks to a few months.
After that stage, he usually begins to notice that I can be somewhat emotionally cold. He gets demanding of more attention, which makes me feel pressured and back away more. We have more long conversations about this, which normally end with me saying, "I just can't explain it to you. I don't know why that is how it is, but I can't change it." He is sometimes accepting of this answer, maybe hoping he can somehow overcome it all and turn me into the nice adoring, loving person he sees me as. And this is where the problem comes in. From the quirks he originally found endearing, he's somehow created a mental image of who I am, and is unable to reconcile the fact that I am not this person he has created.
Normal conversation at this point:
Him: I missed you today, did you think about me?
Me: Um.
Him: You didn't think about me, did you?
Me: I was reading.
Him: But I think about you no matter what I'm doing.
Me: Yeah, but I told you - I kind of have to force my focus.
Him: Do you even care about me?
Me: /sigh
It's normally going into the, "You don't make me feel loved." conversation at this point, and I get frustrated. I have no idea how you actively make someone feel loved. My frustration grows, and I separate myself more and exacerbate the problems by doing so. From here, it's normally fairly downhill.
I've only had one relationship that I wish I could have continued. I'm not quite ready to give up on them yet though. I enjoy them in the earlier stages, and hope that eventually someone can see me for who I really am instead of who they have created in their mind.
Nomaken, I'm sorry if this isn't the answer you wanted. Relationships are so extremely complicated for me, and I went back and forth about answering, but I think it's a very valid question and wanted to give it a try. It's depressing for me to read what I wrote. Hopefully it isn't for you.