Turns out, yes, that I am a stepmother and there's a whole world of self-help literature out there which legitimates the Evilness of Stepmothers (Wednesday Martin's Stepmonster, for instance, which points out, among other things, that while kids don't want a stepmother, most women don't set out in life wanting to be stepmothers either) or which argues that stepmothers have some awful issues with boundaries, norms, and resentments to traverse (see Katz's The Happy Stepmother which paints a picture so bleak about stepmoms feeling disenfranchised, shut out, and reviled that one amazon reviewer says she read the book and promptly broke up with her boyfriend because he had kids and she didn't want all that bad stuff to happen to her).
Really the issue du jour for me is how BF and I interact with each other and continue to treat each other as the apples of each others' romantic eyes when there are children present. Maybe it's an impossible thing: if kids are there, they are paramount. My kids are paramount to me; his kids are paramount to him, especially because we miss them so keenly when they are at their other homes, and especially because we feel so guilty about making them children of divorce. To a certain degree, if my kids are home, I ignore BF; if his kids are home, he ignores me. "Certain degree": how much should this happen? How much should it not? I don't know.
But but a troubling ugly truth is that my kids are not paramount to my BF, and his kids are not paramount to me.
Therein a big difference between our relationship and that of a couple who biologically shares children . . . For the bio-sharing couple, it's easier to make sacrifices for the kids and for the adults' needs and emotions to take a back seat to the needs and feelings of the kids because "the kids" belong to both. Also the bio parents have tolerances and blind spots for their progeny, a generosity and non-judgmentalism borne out of deep irrational filial love. Stepparents see too clearly the small naughtinesses, deceptions and flaws in the behavior of their lover's kids.
Ugly truth #2: self-sacrifice for someone else's kids, even if you like them well enough and might even love them as time goes by, is hard. Or at least it is hard for me.
I think I am a selfish person in wanting to be important to BF even if BF's kids are home. But I Do. I think I am fairly good to his kids and am lucky that I like them, that on the whole they are funny, quirky, interesting beings that I am happy to talk to, happy to be curious about and feel sincere affection for. But also, I conceal too poorly my irritations about things they do differently from my kids, and differently from me.
Anyway, there is much to think about. And much literature out there. And I am not alone, which is a pity because company in such astringent emotions means there're too many edgy stepmoother, strepmurther, stepmonsters out there and the challenge (from where do the resources come??) is to be more like a Fairy Godmother (to my stepkids), UberMom (to my biological kids) and Wonderful Girlfriend (to BF) all rolled up into one package.
Truth #3: Good Luck with that; it seems there are few precedents.