I don't think you choose a partner because of it. However I can imagine being with someone who isn't into it could create a bit of distance in the relationship, feeling unsatisfied, and perhaps sometimes feeling a bit weird about it all. These feelings can then snowball.
Although if there not into it but realise it is a big thing for you and indulge you sometimes it would be OK.
I don't think WAM is all that common so you introduce a partner and it goes one of two ways.
Nope, I didn't tell my wife about my wam fetish until after we were engaged. I wish I'd told her sooner, but her willingness to wam (or not) was never going to stop me wanting to be with her.
I'm poly, but I met my fianceé in the kink scene at a munch. We kind of just instantly clicked, somehow, spent most of the night talking and by the end of the night I'd invited her and a couple of her friends to what was *intended* to be a sort of anime-and-pizza girly sleepover at my place.
For whatever reason, the friends didn't show; so we chatted for a while, lost track of time for a bit, and at some point we were chatting about our kinks. I mentioned this, because it's my biggest, earliest, and more importantly silliest kink (though I can enjoy it innocently too, it's really all about the situation). She laughed, said she'd like to try it; I said I probably have a carton of custard in the cupboard somewhere if she wants to; she agreed, and she enjoyed it, we enjoyed it, we had a really good time that night, and ... yeah.
That's... kind of how we started. We've been together more than a decade now.
Maybe if I'd dated more it would have become something I looked for. As it was, the first girl I went out with, in my late twenties, was gorgeous, interesting and we fell in love. Sex followed soon afterwards, and then we married, but I didn't think to mention the fact that I'd find it quite exciting to mess her up until a year or two into our marriage. Fortunately, her response was "If it turns you on then let's try it", and over twenty-five years later we're still married and still WAMming regularly! I think we'd still be married if she hadn't been up for it too, it's not that big a part of me. But I'd actually credit WAM with keeping our sex life exciting and interesting, even after really quite a long time together - there's always a new mess to plan!!
No we were childhood sweethearts who ended up getting married after about maybe fifteen years of being together since childhood/our teen years, neither of us knew about each others fetish until fairly recently and now we try to wam together at least once a week, but for us it was technically a on the job meeting as child/teen actor and actress!
Love you, too
she enjoyed it, we enjoyed it, we had a really good time that night, and ... yeah. 
