I've done a lot of the same things here. Also had to deal with wanting to eat it so bad before I cum then losing the desire. I would do bent over positions with my cock over my face to force me to do it. I started to do a roleplay in my head where me after I cum was a different person, a very whiny person being "forced" to eat my cum and that really turns me on.
First time I did it for a woman was on a webcam on Yahoo chat. She watched me and loved it. When I met her in real life, she made me go in that position and pegged me while her friend watched. It was amazing. I squirted all over my face and in my mouth. She licked some off my face and we shared my cum in a kiss after.
My (ex)wife liked to snowball me occasionally also, but I let her know she had to be forceful. Doing so made me push through and by the time she had fed me all my cum, I was horny and hard again.
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She really loved when I ate my cum out of her pussy too... She had intense orgasms when I did that. I used to do it pretty rarely. I'd often promise I would, but then back out after I came. Eventually, she got tired of my shit lol. It turned from an ask to a demand, and she would shove my head down there, wrap her (massive) thighs around my head and make me. Again, this was enough to push me to being horny again and enjoying the experience.
For a long time after that, still, however, Anal became an out. She didn't want me back there so if I came in her ass I didn't have to eat it. That is, until she started getting REALLY into rimming. (I have another story here on that) Then after that point, I was no longer safe. I always knew, it didn't matter where I came, it was (is, I guess, still applies after the divorce just doesn't happen nearly as often) my duty to clean her up after and eat all my cum and I was no longer getting out of it. She seems to get even more into it when it's in her ass, telling me to suck it out, slide my fingers in and "scoop" my cum out of her ass and suck it off of them. I love it and now look forward to post orgasm sexual activity.
Solo, I have also recently done "ruined" orgasms as well. I have managed to cum three times in a row, tasting some, continuing jerking with the rest and it also feels amazing.
I can't say I'm 100% past the losing interest, but I can push through it 90% of the time now and thoroughly enjoy it .