My lovely ex's Mum was devoted to his Dad who sadly died of complications to lung cancer and they were all devastated, and she had npo thoughts to look for someone else at all as her marriage had been a real love and soulmate match, however someone suggested because she was lonely that she went to a bereavement group and there she met someone who had recently lost his wife again a real love match, and they just fell for each other. this is now 4 years ago, and they are still together and have the most lovely life and adore each other, but not to the detriment of their previous marriages, so yes I think it happens when it comes out of nowhere, and it's lovely it in no way has diminished the love they had for their partners.