Knowingly or found out later? I had a live in girlfriend back in 1971 when I got back from a year of combat in Vietnam. I did not love her but I moved her into my house and supported her. We were good friends and we both shared a very high libido. Hers was much higher than mine as I found out later. We would have sex in the morning before work, and then after we came home from work, again before bed and usually she would wake me at 2 or 3am for more sex. She wanted sex all the time and was wearing me out. She started to go out with her girlfriends a few nights a week and I went out with mine. I had a lot of living to catch up on and some of that was guy stuff with men I served with in Nam. I always came home before her since I had to get up very early for work. She would come home a little tipsy and tell me to get naked. She would then sit on my face and tell me to make her cum. So far so good and I enjoy oral more than intercourse. A few times I tasted something strange but familiar. I ignored it. It took me a few months before I realized that I was tasting semen. I asked her and she said she was having sex with other guy since we never said we were exclusive. She was right because I knew she was having sex with her girlfriend every weekend and probably her girlfriend's sub. I occasionally had sex with girls on the weekend when she was away. It did not bother me and it turned me on a little as the old sperm competition thing kicked in. After oral I would have vigorous intercourse with her. We continued like that for many months. One day she entered the living room where three of my friends and myself were watching a football game to announce that she wanted us to gang bang her. That caught me by surprise as it was understood that we do not have sex with people we both know. My friends looked at me and I said OK. However, they did not want to get naked in front of each other and have sex. Most guys think it is easy to arrange a gang bang. It is not since most guys do not want to get naked and erect in front of other guys who may be bigger and better. Many could not get erect under those circumstances either. She then said she would perform oral sex on each of them privately in the guest bedroom. She wanted me last. When my friends were done and looking embarrassed for me, I was called into the bedroom. She was covered in cum from her mouth down to her vagina. She purposely made them ejaculate all over her because her plan was to have me lick it all off before having intercourse with me. She said she thought it would be even more intense since I knew the other men. That is the day I learned my limit and and refused to lick her. Instead I let her perform oral on me and asked her to leave the next day. I found out that she was having sex with one of those friends, maybe two for a few weeks without my knowledge. That was not the last time I ate semen. The next time was after a wife swap when I ate my best friend's semen from my wife's vagina. I presume he ate mine on his wife's breasts. The sex was very intense as usual when I taste semen on my woman. Then my wife got into giving me oral after I had sex with her or my girlfriends until she came out as bi. Then we had a threesome with my wife's best friend and had her live with us for the next 7 years. My wife enjoyed the threesomes and both enjoyed having sex with me after the threesome. So they were tasting me and each other all night long. Then our girlfriend got married to a cuckold and I was her "bull" but really her lover. She shared me with my wife. After that she split her time between me and her husband. I never tasted his semen because I my girlfriend did not have sex with him for 3 days before seeing me but the reverse was not true. She never said much about her sex life with her husband other than they had an arrangement. Only once during one of the vacations that we allowed her husband to join us, that I tasted his semen. His wife would stay with us all day and only be with him after we were done for the day. I specifically asked her to have unprotected sex with him right before she came to our room for breakfast. Apparently she had him wearing a condom because neither of them wanted kids, like us. She let him cum inside her and my wife and I took turns performing oral on her. We like to get kinky once in awhile. It was OK but he did not cum much and what little there was, stayed in her panties. Nonetheless there was a faint taste of semen mixed with her her lubrication and that is the way I like it. It is like not liking Whisky straight but add two parts water and I will drink it as it tastes mostly like water. That was about 20 years ago and I have not tasted semen again. I tried to get my wife interested in a MMF threesome but she is not that into guys unless they are young and hot. Not fussy about women though. I had sex with two males before I got married but it was not oral sex, just anal so never got to perform oral on a guy and still have that on my bucket list. This is a long way to say that I have both knowingly and unknowingly tasted semen. I was never into what I see in porn which is mostly fake, where there is a waterglass amount of semen in or on the woman and the guy eats it all up. Not my thing. Mixed with two parts female juice, I can enjoy it.