Everyone's sex drive ebbs and flows and gets stronger and weaker as the years go by. I wouldn't worry about it, but I would try to talk to your partner about it, not when he is wanting to have sex, but in a neutral setting, like right after dinner when you are cleaning up. Communication is...
Did you use a water conditioner when you cleaned the tank? The chlorine and heavy metals in tap water can be deadly to fish, although some have a higher tolerance to it than others. I'm sorry to say that I think your fish is dying or might already be dead. Watch his gills to see if they are...