if you think he has feelings for another , and by your own description regarding his " shuffled answer" then the answer is yes. Then he isnt free as in without feelings for another and this will mean that this " friend " will always be something for you to worry over " even if nothing happens " . The question is can You stand being in a relationship where your not totaly sure your the " other half's " most wanted .
Personaly i would walk away now , but thats me not you .
Only you can decide what action to take and if your prepaired to be unsure if you will come first always as regards to your partner , and its your feelings that will always be weighing up if your sure he considers you above all.
Hard one to answer but if you look inside and know you can or cannot be in such a relationship with / without such worries , you will be able to answer this qurestion yourself.
hope i have managed to elaborate what im trying to say here.
what ever you decide make sure its what You want and For Your best .