These fantasies are common, especially in the domain of cuckoldry.
One element and variant in cuckold psychological make-up is that of channelling the wife’s pleasure - in essence, “becoming her.”
In turn, this can lead to sub, or submissive acts; sucking her lover’s cock, touching it, being fucked by him. It may include sissification, even extreme cross-dressing and total feminization.
I have an extreme cuckold acquaintance who actually emulates his wife; dressing like her, hair/wig, make-up, everything. He participates in their encounters as a sub, taking the rougher stuff on her behalf.