I was in
Icmeler in May last year and the weather was fantastic, up in the early 90s, even wasn't too chilly in the evening, don't recall needing an cardi, though you wouldn't want to sleep with the doors open.
May the year before was much more mixed, more cloud than sun and definitely chilly in the evenings - borrowed a pashmina from Elvis in the Chef a couple of nights

They're certainly well equipped!
So it could be great, or it could be mixed, but whatever, you'll have a great time, I love Icmeler in May, it's my favourite time (though if I'm honest any time is my favourite time there - especially my 2 weeks in September lol!)
Have a brilliant time. Due to other commitments I'm unable to get there in May this year

Oh well, only 21 weeks till September
Mazz