Is he or isn't he cheating?

My husband of 25 years asked me for a divorce on Valentines day, while I was making a dinner for two.
He says we have drifted apart and doesn't want to try to fix things. He wants this over with quick, he claims it will be better that way. The next day he set up an appointment with an lawyer,the next day he got an apartment or himself the next day he moved out now today I'm still searching for answers because I have to go see his lawyer this afternoon.

I asked if there were someone else and he said no. I want to believe that, but everyone I have talked to seems to think there must be for him to want this so bad so fast. he's always been a good husband to me and our children.

My suspicion is there is, because he does go out alone every weekend. Sometimes for a few hours sometimes longer. But every weekend without fail he goes. Other then the weekends he came home everyday from work. No weekend trips, no cell phone calls, no secret talking on the phone, and he doesn't use e-mail (from home).

Does it sound like there is another woman? Why does he want this so fast?