I used to have a "one dick" rule, but recently with my current partner (we're middle-aged, she's childless by choice, I have kids by a previous partner) I feel I'd be totally OK with her having sex with other men. From very early in the relationship, we were very open and communicative. I know she can come from PIV, as she's told be she has, can and did. I've never been able to get her to orgasm with my cock, tho. Of course I give her G-spot orgasms with my fingers and eat her clit until she literally screams with pleasure, but I feel she's missing out on a good hard fuck orgasm. I'm not sure why she can't come on my dick, we're a good fit, I get very hard, can go for a long time, hard and fast, as she likes it... but I know she dated two black guys over the years and they had huge BBC's.
If she can get some amazing pleasure from a big dick, but I can't get her off with mine (I've made plenty of other women come on it, so I hold no insecurities about my size or skill) who am I to stand in the way of her receiving that pleasure? Seriously, who am I to stop her from getting a crazy hard orgasm from a giant dong?
She has no interest in doing this tho. Either with or without me being there. She believes in being with one man (although she has had a MFF threesome with a couple before). So it's not a matter in our relationship, but I, now, sincerely, for the first time in my life, would not be bothered and in fact would revel in her pleasure, seeing her come on another man's penis, because I love her and want her to have pleasure. If she was sucking my cock, or I was in her arse while it happened, so much the better. Well, maybe it's not the first time I would be ok with it. I was dating another woman a while ago for sex alone. We weren't couple material but really liked each other's kinks. Hers was receiving bukakke. We never got around to finding certifiably clean men to jizz all over her, but that would have been hot as hell. I would have loved to watch her suck all those dicks and catch the come on her face, so long as mine was the first one.