@Frazzledfiona.
You say that you feel bad that you don't love your parents more, but is it that you don't love your existing parents, or that you wish you had parents that were loveable?
My Dad is an arse. He was a shithead to my Mum, he's utterly self absorbed and I honestly wouldn't be bothered if I never saw him again.
I'm nice to him ( as long as he's not being a dick), I'll go out for a pint with him every so often, but I don't particularly want more of a relationship with him. When he dies, my reaction will probably be the "Oh dear.... Anyway" Jeremy Clarkson meme.
My Mum on the other hand was caring, supportive, actually enjoyable to have a conversation. Yes she pissed me off sometimes, and we had some rows, but I felt bad when I upset her, and she was always the person I'd first go to for advice.
To the outsider, I probably wasn't seen to grieve that much when she died, but I was angry for a while (because I am a man and therefore have the emotional intelligence of a 3 week old chimp). 2 years on I still find myself missing her intensely at times.
There's probably a fair few people in your life who your entire relationship with could be summed up as "Meh!" (Work colleagues are a good bet here, you spend 8 hours a day with them but you don't really care).
People act like you're not allowed to be "Meh" about family, but why not? You don't love them because they've not been particularly good people, but you haven't fallen out with them, so they're somewhere in the middle. If they weren't family, you'd have dropped them long ago.