My DH works in an office environment and has done for about a year now. A few months ago he started mentioning a girls name all the time but I just thought he was trying to wind me up.
At christmas they all went out for a christmas do and after that he started to panick every time the phone rang, would smuggle his mobile into the toilet with him and started putting passwords on the PC etc so I started to get a bit paranoid.
Last night I went to bed early as I wasn't feeling too well, I suffer from insomnia so wasn't expecting to sleep, just rest.
After an hour or so DH crept upstairs, came in the bedroom and stood looking at me, I had my eyes closed and pretended I was asleep (incase he wanted sex! ) he then began to whisper my name as if he was making sure I was sleeping, I didn't respond.
After that he crept back downstairs and after a few minutes I heard him talking on the landline phone, I couldn't really work out what he was saying but he was blatently talking quieter than normal and laughing a lot.
I let it go but curiosity got the better of me and once he'd come to bed and gone to sleep I got up and looked through his phone and there were loads of texts from the same girl (a different name to the one he'd been mentioning though). Nothing sexy or 'raunchy' but alot of pisstaking such as a message from her saying "why what size is she? lol" and a reply from him saying "not sure i should say, bigger than u anyway!". Another one from him saying "she whinges about everything anyway so I probably wouldnt notice!" and a reply from her saying "lol bless her ;)".
Both my dh and I have platonic relationships with friends of the opposite sex. We have been to concerts/played sport etc with friends' husbands/wives. This sounds very different to me - especially if he is putting you down by making adverse comments about you.
You need to confront him - try not to get too angry, though. It may not have developed into a physical relationship yet. It sounds as though things aren't 100% rosy in your relationship, so if you want to move forward it is essential to start talking through your issues.
how long have you been together and what were thing like before he started mentioning this woman?
my personal opinion is that you have every right to look through his phone as he is giving you plenty of reason to be supicious.do you know for sure the texts were about you,though,that they weren't slagging off another collegue?
it sound like you have been suspicious for a while,if you pretended to be asleep.
He's actually not being terribly discreet, is he? If he wants to have an affair he should be a bit more clever about it - buy a separate phone etc. It almost sounds as though he doesn't mind if you find out.