How long have you two been friends? Since he's engaged he may feel a lot more comfortable about being able to say what's on his mind to you. Why? Because you know he's engaged and he wouldn't/shouldn't be trying to make moves on you and since he's engaged you won't classify him as a creeper...Hope that made sense...
He may have had feelings for you in the past and never really got over those feelings. However, he's engaged and you should respect that. If he makes a move on you remind him about his engagement and let him know that you'll be there for him as a friend and friend only.
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