—Always a bridesmaid
I obviously don't know your fella, but in my opinion, weddings are simply fancier and longer versions of regular dates. They don't have to be laden with meaning, nor do they signify that all who attend are secretly vying for a lifelong commitment. That'd be like inviting someone to a horse race and being disappointed that you didn't come home with a pony. I know, I know, there are a lot of overt declarations of love at weddings, and this can make people squeamish, but seriously, the only "commitment" you're asking for is a few hours of his time and that he please change out of his velour tracksuit for an evening.
Play up the perks of being a plus-one—free food, open bar, post-wedding sex!—and minimize the less than thrilling aspects—the time span, the drunk speeches, the inevitable and awkward moment when someone's uncle asks, "So when are you two getting hitched?" This question is unavoidable. Expect it to be asked, even if your plus-one is a houseplant. (What? 2008 was a hard year, OK?)
A caveat: If any or all of these weddings are out of state, then that ups the stakes. Asking your dude to spend several hundred dollars on a couple he probably doesn't know is a lot to expect from someone you're casually dating. But other than that, it shouldn't be terribly risky to ask. I wouldn't, however, invite him to all three weddings at once. If someone I was dating asked me what my Labor Day plans were in June, I'd wonder about their presumptuousness. So invite him to one and see how that goes. Get down on one knee before you ask him. Guys love that!
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