I need to break someones heart and feel dumb...

Fuck!shit!fuck!

I (34f) got involved with a 25m guy.. for fun ! Clearly stated for fun..

Things got waaay too deep to quickly! he basically opened up about his whole life to me, started doing really sweet things (you'd expect from a boyfriend/ husband, but not a whatever relationship) and after a couple more weeks he is now totally head over heels in love (told me) ...

I saw that he's kinda falling for me, but I thought maybe I'm just imagining things, since we agreed to be casual.

I feel so dumb and like the biggest btch. I need to let him down gently, but how? I don't want to hurt him.

Was thinking about continuing a bit more and maybe his rose colored glasses fall off by themselves...

Advice?

Edit: thanks for your replies. I'll rip the band aid off and let him know my stance tonight.