Maybe is fluctuates according to our level of acceptance, of the loved person or thing. Maybe it fluctuates when our own self esteem does, or certainty? Looking at myself, I can see where that happens sometimes. Probably happens other times, and I just don't think about it.

I think maybe I think of it in reverse to what you said, compassion is part of love, and love is not always part of compassion. I can feel for someone's suffering, with out extending love. Maybe depending on the things I mentioned above, at least in part. But I cannot love without extending compassion, which is basically empathy. To me compassion is just one ingredient in love, but an important one.

Maybe it just has something to do with conditional love? I think we all like the idea for the most part of unconditional love, I am not sure tho if that is the way the human mind operates naturally.

Personally I chose not to worry about love and compassion and just put my focus on awareness. You can't really measure love or compassion but you can determine if you are letting the same things get to you less frequently, or if you are catching yourself sooner. Love and compassion aren't really things to develop, anyway; you uncover them.