How should I respond to his message after finding out he has a gf?

[mainelobster]

I've been casually seeing this guy for almost a year now. We agreed from the beginning to keep it casual/FWB. I've explained to him in past conversations that a boundary of mine is that if either of us gets into a relationship to let each other know, as I prefer to be sexually monogamous. Last night we went to a mutual friend's birthday party, and afterwards we hooked up & spent the night together. We cuddled all night & morning, and after I left his apt he sent me a text saying he had a lot of fun, thanking me for coming over. Meanwhile, I did a little bit of social media snooping and discovered he's seemingly in a long distance relationship with another girl. He hasn't posted any pics of her to his page, but there's a picture of them together on HER page and it's very obvious they're a couple. I want to respond to his message in a way that acknowledges I had fun, but that I know about his gf and basically break things off with him. Is this a good text to send? 

"yeah I had a lot of fun but I was wondering if you think we should continue to see each other? I like you a lot but I've noticed that you're dating (*insert other girls name*), and it makes me question if I should still be seeing you. She's so beautiful and I don't want to be the reason that she's not getting your full attention. And please don't worry; I won't ever tell her about us as I have no intention of breaking apart a relationship. I care about your happiness and I don't wanna complicate things or be in a situation where I feel like a side chick. If circumstances change in the future, maybe we can reconnect."

Should I send this or should I just go ghost?

[MissCanuck]

Girl, no. Do not send that.

Simply tell him you can't continue seeing him knowing he has a girlfriend. End of. The rest is too much. 

[Wiseman2]

11 minutes ago, mainelobster said:

 We agreed from the beginning to keep it casual/FWB. he's seemingly in a long distance relationship with another girl. 

Please don't send this message. Don't even acknowledge you had fun.  He's cheating so don't help him out with that. 

Stay true to yourself. Your agreement was FWB until someone is in a relationship and he broke the agreement.

That's all you need to know. Just tell him your arrangement has run it's course and you'll be moving on.