For me, kissing is such an intimate act, more so than sex. I know it makes no sense that penetrating her mouth with a tongue is more intimate then penetrating her vagina with a penis.
I hate it when I see it. The problem is she loves to kiss, it's a major turn on for her, she probably has as many nerve endings in her mouth as her vagina and as many on tongue as her clit.
She's sensitive to my feelings as she rarely kisses her partners, but there are times she does and I try to be sensitive to her feelings by saying nothing and trying to hide my displeasure.
Before we entered the lifestyle I'd tease her that any if a guy got his tongue in her mouth he'd be able to get his dick in her pussy. She'd smile back at me. Little did I know all it took was having a dick, kissing was a bonus, an extra.