<human>: Can you give me a shortened version of the text?

Firstly, if you want to judge me or call me a slut for being in an open relationship, you can leave now. Every relationship is different and this is what works for mine. We've been together for more than eight years now, married for two, and are madly in love with each other. 

Okay, now for my dilemma. I met a guy several weeks ago and got his number. I've been scared to call him though because I have no clue how to tell him I'm already in a relationship and am only looking for a fling. I've only ever done this once before with someone who didn't already know about my situation, and with him, I lied. I don't want to do that again. 

Do I tell him before we even go out so I don't waste his time in case he's not interested? Do I tell him the first time we hang out? And how do I explain that I'm only interested in casually hooking up? I have a problem with being vulgar and I don't want to just come out like, "I'm only lnterested in fuckin' aight?" Any advice is appreciated reddit.
<bot>: How do I explain to a guy that I'm already in a relationship (but it's an open one) and that I'm only interested in casual sex/a fling?