Matt, it's not clear to me just what your question is. If you mean will being fucked by a man with a big penis affect your wife's health, no--assuming he doesn't perform like a battering ram and injure her physically. If you mean will she contract some health-undermining STD--depends on whether her fuck buddy is disease-free. If you mean will the larger penis expand her vagina permanently to the point that your smaller member is not clasped tightly enough for successful intercourse, thus affecting all aspects your marriage--not really likely, especially if she is in good health and physically fit. It might be good insurance for her to perform kegel exercises regularly to help prevent such problems...and for you to do the same. -- But, that having been said, you actually appear down not-so-deep to be troubled (not surprisingly!) by your wife's extramarital affair, no matter how accepting you may want to seem on the surface. A frank, heart-to-heart discussion might be in order: Does your wife love you more than she loves her buddy's big cock...is there anything other than raw sex involved between the two? After all, she married you with, I'm assuming, full knowledge of your size. If a discussion (but not a violent confrontation) does not help, you might be well advised to consult a marriage counselor--again, assuming that the two of you sincerely want to stay together. ~~ A tough situation, friend--best of luck to you.