Eh...no.
I understand this is a VERY common misconception (and this was the apparent justification for the rage-inducing final scene in Unjoined), that Ezri was just Julian's "substitute" for Jadzia--but frankly, it is completely false.
Ezri actually destroyed any chance of this happening by her moment with him in "Afterimage". To be honest...I think her moment when she said, "If Worf hadn't come along, it would've been you," was a real wake-up call for Julian.
You can see him struggling inside, torn with emotions within. I, personally, read his thoughts thus, Confound it, Jadzia...why didn't you ever tell me? Was it a game for you, that I wasn't skilled enough to see? Why didn't you ever give any indication...that there was something more?
Or thoughts to that effect. The point is, it was a wake-up call, in that Julian finally realized that, if he was not eager enough to keep trying for Jadzia--when if he would have, he and she would have gotten together--that it wasn't truly love, just a fool's infatuation on his part.
Now...as for his relationship with Ezri, note carefully how the relationship developes. For most of the season, they are very dear friends, building each other up when down, enjoying each other's company, and the like.
In "Strange Bedfellows", as Julian reflects on the missing Ezri, he mumbles, "Funny... I was just starting to..."
When O'Brien asks what he's talking about, Julian says even he isn't sure what he's saying, "But...there was something about her...wasn't there? She's this old soul...and yet, so young at heart...."
It was at this point that Julian begins to realize he's fallen in love with her. Had she been a "substitute", he'd have been entertaining thoughts about this long before. Not until long after the two have become very dear friends...does he fall in love.