If you are looking for a shorter, more personal review (e.g., for social media or a conversation):
If any of those are true, you aren't just "loving" your FIL. You are using him as a weapon to punish your husband for his shortcomings.
Let us be brutally honest. Sometimes, the reason you love your father-in-law "more" is that your husband is a bad partner.
You can love your father-in-law deeply for the man he is, but it should never come at the expense of your partner’s dignity. If the gap between how you feel for both men is widening, it may be time for a transparent conversation with a therapist to figure out if your marriage can be nurtured to provide the same sense of security you’ve found elsewhere.
The first thing to understand is that the English language does a poor job of defining love. You love pizza. You love your childhood pet. You love your husband. You love your father-in-law. These are four different biological and emotional events.
Generally, no—unless you can frame it constructively. Instead of saying "I love your dad more," try: "I really value the way your dad listens to me, and I’ve realized I’ve been missing that kind of connection with you lately. Can we work on that?"
You do not need to stop loving your father-in-law. That love is a gift. But you need to redirect the energy.