Hello all.
I'm a first time cat owner, we adopted a friends cat as she was moving to UAE in March.
Henry came to us as a bit of a nervous boy, 7 years old and had been bullied by our friends other cats. We were told he was an outdoor cat most of the time. We kept him in for well over a month to get used to us, he would hide during the day but stare out the windows and be very active and affectionate at night, and especially towards me.
After a month we took friends advice about letting him out but he was having none of it, he would run straight back in and hide. So after two weeks of this we gave up and just figured we'd return to life as normal.
Henry carried on staring out the windows and mewing at us, we'd offer him the outside world but he'd still run away from it and hide in the house. Last night we had a big moth appear in the living room, so we opened the patio door a little (never really opened it since we had Henry) to let the moth out. As the breeze was nice we left it open, Henry got up wandered round the living room a little then just walked out!! We were totally shocked! This was 11pm though, we left him about 5 minutes and then went to call him and reward him, but he'd gone. We have a massive garden that backs onto woodland and behind that a timber yard.
It's now been over 12 hours and I am so worried about him. He's still a real scaredy cat sometimes, I'm so worried that he came back in the middle of the night trying to come home and couldn't get back in (we don't have a cat flap or capacity for one) and has now run away.
Am I being silly like my husband says? Do you think he'll come home? 
(Sorry for the long message!!)