its not exactly something i would be willing to risk. there has recently been a post about breeding pairs attacking each other.
you could come home to this ...
http://www.albinoburmese.com/forums/index.php?showtopic=772&st=0
not eating is a strong sign that something is wrong with the argentine. and it doesnt have to be a perfect world for you to provide the best for your animals that you can. in my opinion you should not have two snakes if you cant afford two cages, but that is just my opinion. you could make a cage for probably around $100 or less. if you are located near me (either state college pa or lafayette hill pa) then i would gladly help you make a cage and all you would have to do is pay for materials (like i said under $100).
but lest be fair here, you asked for opinions on why your snake has not been eating correctly and to me that is the most prominent reason why. i too have managed the reptile department of my local pet shop for a few years and had no choice but to house multipe snakes together (as it was ultimately not my decision). its a chance that there is no need to take if it can be avoided.