Has he given you any reason to believe that he is cheating on you?
How long before he goes back on your shift?
Have you talked to him about it? If so what was his response?
It's only a couple days until he is back on shift with you, so I would not be too worried about it. Sometimes he should make time to spend together, maybe making sure you're plans don't go so long that he can't stay awake.
You have to by what you feel, what your woman's intuition is telling you, instead of listening to your friends. They are not in your relationship so may not know everything that's going on. Sometimes friends can be a help, but sometimes they just need to let you figure things out.