There are already two completely exhaustive answers, I'm waiting for my tea to cool down and I'm bored.
So, with the exception of pregnancy here and now, all that one partner can reward with is sexually transmitted diseases.
Well, there is by the way another nuance, that in the body of a woman can be found the cells of her born children, which contain 50% of the father's genome. But this has nothing to do with telegonia, well, in any way, if only because these are the cells of her child. In theory, this could affect future offspring, but only through the mother's immune response. And this could hypothetically have some effect on the offspring in the event of a Rh-conflict, for example. But in this case, it often does not matter at all whether these children have one father or three different ones.
But sex that did not lead to pregnancy can only reward you with a bouquet of different infections and / or psychotrauma. These are real dangers.
It is very difficult to stretch the simple correct answer "no, this is all nonsense of a gray mare who fell ill with a moral plague of the brain" into one hundred and forty printed characters.