Well in all honesty I wouldn't know, never been in your shoes, but a few ideas come to mind.

You could create a manic check list.
If you're experiencing all your other classic symptoms of mania as well as this impulse to cheat, then you very well may be manic, and should alert your pdoc who may want to tweak your meds for now.

If you're not in the midst of a mood episode, you could either just need some intensive TLC from BF, be a serial cheater, or be a polygamist at heart...

Goodluck!!! and to our little crazy corner!