Sorry I didn't get to see what you had written before I took off. I'm back for a little while. Hmmm fireworks. So perhaps she was married for nigh unto 30 years and was quite jittery in the beginning way back when. Or even had some butterflies with one of the short termers since her divorce, that fizzled because he was wrong or she wasn't ready or both.
Have you done anything together that was really scary, or at least very exciting, like skydiving first jump, or dealt with a dangerous situation together? Or stood by her in great sorrow? These emotional experiences intensify love. It's possible that astrologically the spark was not there even at first, and that doesn't preclude love lasting forever. Or it was there (you'd know, I'd guess) and it's been stifled under her fear of repeating old mistakes. Diving in and then diving out is normal for recovering divorcees. Any astrological matchup except what erupts early on in violent conflict or loathing (& actually violent conflict is dangerously compelling) is subject to the couple's desire to build a solid foundation. And if her husband treated her badly & then "repented" that would have made fireworks a lasting infection.
It's also possible that you ARE too nice. That you need some WildMan in you that can't be tamed, that NEEDS to go off and do your masculine thing & no domestication can take that away from you. If you're too compliant with her desires, and you grew up under a newly feminist mother, you might be what Robert Bly called a "soft male" who doesn't assert enough for fear of offending his woman, so she gets an uneasy feeling that he's a wimp, or he's hiding something (which she can't name, because WildMan isn't a household word). Bly's book was Iron John (1991 I think). Is there anything that you do that you WOULDN'T give up if it bothered her, even tho it wouldn't impact her except for losing some time with you that she might want.
If a man doesn't seem to ever need time away from his woman, but only goes along with her wishes for time away from him, she can come to feel like he's holding onto the hem of her dress. These are just possibilities I'm throwing out in case they might apply to her "sparklessness." If that's possible, then one good solo venture of your own that you're gung ho about doing, even tho it might interfere with some plans she'd like to make, could do the trick. Showering a woman with kindness alone doesn't keep a woman interested if there's not some unpredictability about you, and some pieces that can't be bent into the right shape for her taste.