Shouldn't Edward Elric still be able to perform alchemy?

Question

The reason I ask this is because Edward had his own portal of truth that he discovers after leaving Gluttony, but that's the first time he notices it. The first time he meets Truth, there's only one gate. Unless that first gate was Edward's portal of truth, and Gluttony was like some weird second door that gave him a sort of secondary exit, wouldn't Ed still be able to perform alchemy?

We never really learn what the two different gates mean, other than that one is Edward's portal of truth. What is the other? Has it been there the whole time? (Is it the one he used when he was little? He performed alchemy then, didn't he? With just one portal of truth, that, for all we know, wasn't his? Is this making any sense?) He gives up his portal of truth, yes, and all that should do is make it so that Ed can't go hopping back and forth to see Truth, as that was the access the second portal kinda allowed.

Answer 1

The Portal of Truth (or Gate) that Ed finds after leaving Gluttony is not his Gate. Rather, it is Al's — this is why Edward finds Al's body sitting in front of that Gate. This is later acknowledged by Ed when he remarks that his and Al's Gates are connected and that this is how Al's body is sustained. The Gates were not always connected; it's made clear that it's unusual and that the connection is a result of Ed's exchange at the beginning of the manga of his arm for Al's life.

When Ed sacrifices his ability to perform alchemy, he is giving up his own Gate. Normally this would not be possible, as this would mean losing the exit back to the real world (cf. Why can't Roy Mustang bring his eyes back using his gate?), but since Ed and Al's Gates are connected, Ed is able to return via Al's Gate. This doesn't mean that he can do alchemy, however, because one's Gate is personal and tied to one's potential to perform alchemy; Truth refers to this in the exchange after Ed decides to exchange his alchemy for Al's body.