yup, did this in university, only I was the woman. It isn't all that uncommon at younger ages... or it wasn't in my life anyways. Now I think it is even less uncommon to live with roommates and then start sleeping with them.
I agree largely with Sch, get some education under your belt by reading on here and elsewhere. There is lots to learn and it's all very la la la when things are good, but they can go fast the other way. Find out how they can and talk about it with them. What are their fears, what would they like to see happen if this doesn't work out... etc.
It's all very well to casually have sex with friends you like, but poly is about love and a level of commitment that is deeper. It's not just sex. Make sure you are ready for all that comes along that isn't sex. Of which there is many and most of the relationship. The actual relationship part will be a huge part, more than any mono one you have been in.... prepare for that...
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