It's not acceptable to lie to someone you love.
Dan is leaving the house he shares with Julie and doesn't notice Julie's dog in the driveway and hits him with his car.
Dan wants Julie to not be angry at him.
Dan takes the dog to the emergency vet clinic instantly and calls Julie immediately to let her know what happened.
Dan doesn't tell Julie that he hit her dog and disposes of the body before she finds out.
Dan made is to the vet quickly enough that he was able to save the dogs life and tell Julie that he was going to make it.
Julie finds out from a neighbor that Dan hit her dog, and she breaks up with him.