I would say I find personal truth in both versions of love.
For me, love is definitely a source of joy. It also so happens that everyone I truly love has the capacity to cause me a great deal of pain, but I certainly don't characterize love that way. It's more of a biproduct of opening myself up and trusting someone with my heart.
In other words, for me, it's not "I love them because I'm vulnerable to them" but rather "I'm vulnerable to them because I love them."
Just making myself more vulnerable to someone doesn't itself strengthen the connection I feel to them. But in order to truly open myself up to the wonderful possibilities that love has to offer, I must also open myself up to the pain that may come if things go sour.
What we would say in math is that it's "necessary but not sufficient."
I would never presume to "define" love. You know it when you feel it. It's like an orgasm: If you have to ask "was that it?" ... that wasn't it.