How to get a friend to mutual masturbate with me?

We're both straight and are 17-18 years old. We practically grew up together, but don't hang out all the time, it's pretty sporadic. Yet, we are very good friends. We have started a thing where we go camping in the wilderness for a night or two, we are planning a two nighter next week. Last time(the first time we did it), we had a good time and went skinny dipping for a very brief time, the water was freezing. There was no sexual tension at all the whole trip.

I'm sort of in a bi-curious stage, I don't feel gay, I've loved women all my life(and am trying to pursue one now) but feel the want to explore my sexuality. I think he is too because whenever we're doing things together, he slaps my ***, or thrusts on me or something, but I've never done anything about it. We have talked about jerking off and porn before, I know he does and I do too. But never in front of anyone else for the both of us.

I'd just like it if we could be cool to jerk in front of each other. How should I do the ice breaker question? I don't want to lose a long friendship. How can I make it discreet? Thanks!