IF you are married, and IF your husband has acknowledged and/or consented that you are having sex with another man, he has to bear the responsibility, along with you, of providing for any child born of the "illicit/immoral mating". On the other hand, if your husband has no knowledge that you have made a cuckold of him, he can question the paternity. If the DNA testing reveals that he is not the father; your adultery would be legally established. Your husband could sue for divorce; how the court determines how much child support is to be provided by each of you will be decided by the judge. Under either situation, your bull is off the hook. Unless, the bull demands his parental rights be recognized. If that situation arises, all bets are off. This is all summed up by the following adage: "A true alpha-male will fuck/breed any married woman; provided she is married to someone else".
You should discuss your bull's request to fill your fertile womb with his potent baby-makers with your "legal" spouse. If the spouse agrees, all three of you should have a good time.