<human>: Give me the gist of the text in a nutshell

So I am in to outdoors-type things and my gf isn't so much. We both graduated from college about a year ago and have since moved back home. All of my old friends are off somewhere else and the only person I share my outdoors interests with is my coworker, who I would like to consider a friend, though right now only at work. 

I am in an area where it is a little hard to meet people who share similar interests and I am sort of introverted, so naturally I want to hang out with my coworker who I've already befriended and who offers to hang out fairly often. The problem is that my gf is sort of the jealous type and I don't want to betray her trust/piss her off. 

So, how the heck should I try to do the thing that I enjoy most in my spare time (hiking) with someone who will enjoy it in the same way that I do, without irritating my gf or making her jealous? And I'm not talking about backpacking over night, I'm just talking about a couple-hour day hike.
<bot>: I [23 M] want to go hiking with my coworker/friend [25 F] but don't want to make my gf [24 F] jealous or angry... what do?