I don't see how your sexual orientation makes the least difference to whether you are monogamous or not. Unless "pansexual" is just a euphemism for sex addict.
Of course it's possible. There's no rules here, just whatever suits you! Sexuality is a fluid thing and so can be monogamy. For example, I would consider myself pansexual but am only desiring of my current partner right now. This could change at any time, but right now this is what suits us both.