Presumably you've just gone back to being away for periods? I'm not sure if you want reassurance about the nursery, or tips on the periods away? I work PT so I understand your feeling guilty about the nursery - lots of people here can be more constructive than me, though.
It's different, but my DH does a lot of international travel, away for a week at a time. When he's home he is about a lot and very involved, so DS (22 mo) does miss him lots when he's not here. He's just twigged that daddy goes on an aeroplane, and every time he hears one, he says "daddy" and wants to see it.
I think in a few months we'll use some form of wall chart / symbols to show that daddy will be back in 4 days, then tick of a symbol each day.
DH also makes an effort to call at bedtime, and often in the morning, and I put the phone on speaker phone so DS can hear clearly, but we don't push DS to talk to daddy if he's busy doing something else. He claims the cost of the phone calls, or that would be a harder decision. He occasionally calls from a Skyphone.
In a few years we'll get a world map so we can show DS where daddy is, att he moment I just say he's at work, and will be home in x days, or tomorrow teatime or whatever.
Will be interested to see other people's tips as we're finding this tough.