getting regular wet dreams over work colleague

Like most people I used get spells of having wet dreams fairly often while still a teenager then a few random spells when I get several in succession but up until recently they've been very rare.
For some reason a couple of months ago I had a wet dream again which came as a bit of a surprise but since then I've had several more and with increasing frequency. It doesn't seem to make much difference if I make sure I cum before I goto sleep either. My girlfriend didn't pay much attention at first but now it's beginning to upset her. I don't recall actually having sex in any dreams but it usually involves a woman I work with, I never try anything with her or ever cheat but I can't help getting aroused by her. I feel guilty but don't know what I can do to make them stop?