Jealousy after 16yrs of marriage

Hi. I've been married to my husband for 16 years and can honestly say that 15 1/2 of them have been very happy. The last six months have not been so good though. I think with work and children we have lost each other. Now the children are older (13 & 15) we don't get much time alone as they go to bed the same time as us! Also computers, kindles and TV have not helped. We just seemed to have stopped talking and having fun together :-( Perhaps this is normal for a 16yr old marriage but I don't like it. He had also become very distant and I was feeling like I was loosing my best friend. Naughtly I read his work emails. Bad move! He had sent some to his office secretary. In them he had called her 'Babe', 'button' and 'office hottie'. At the end of one he had put 'counting down the days'. He had wrote this while we were on holiday! I confronted him about it and he was very sorry. He said it was just office banter and the 'counting down the days' was because she was due to go on holiday the next week and was fed up with work? This was about 2 weeks ago and thing have been a lot better. We're talking more, laughing together and having great sex! The thing is today he went away with work to do a show. Four of them have gone and she is one of them. I trust him but my head is all over the place and my tummy is in knots. I don't know how to get over all these jealous feelings? Do you think I'm being stupid? Where do we go from here?

its not wrong to feel like that but dont get too carried away,it may be nothing.