I agree with Trippin' -- that's a borderline trait.

In answer to your question, I'm not clingy. (Me: bipolar, yes. Borderline, no.)
I love to do things together and am very devoted, but do stuff by myself all the time (not simply things like going to see music or eat, but also things like international travel and solo driving of thousands of miles).

To compare/contrast with your situation, I also have no relationships with family except my sister, who lives 3,000 miles away. I'm an introvert too. Like you say, the other person becomes a LOT to you, and I can relate to that, but for me, never in a suffocating way.

The only time I wear them out is when hypomanic, lol. It's like hanging out with Tigger. Only worse.