Disclaimer: I just need someone to pat my head and say it's all going to be okay.
I bought my dress early, because I happened to find it, and loved it. I had no intention to buy it right away, but I did, and I don't regret that. I will always love my dress. I did worry about sizing; my weight, never good, tends to fluctuate. The head seamstress swore to me, up and down, that she could alter this dress many sizes either way, whatever happens, when the time comes. It fit when I bought it, and we'll adjust as we need to. So I stopped worrying.
Six months later, I put my dress on again, just to see it, and show two female relatives.

And I can still put it on. Yay! But it's looser in the straps, and tighter in the waist, than it was. I'm standing there thinking, that's okay, we're still good, alterations were always in the game plan, and my wedding is over a year out anyhow. Who knows where I'll be then! But my future stepmother-in-law chose that moment to tell me I needed to join Weight Watchers and do something RFN if I want to be able to wear this dress when I get married.
Yikes! I mean, why say that to me, as I stand there in my dress? Of course I'd like to lose weight by then, but I've got some health things going on (that she knows about) and I'm doing my best with them, and it makes it hard to worry about vanity. My FH just wants me to be happy and healthy at our wedding, and so do I, and I hardly think I need to panic just because my dress got a little tighter in the past 7 months! I'm not being delusional, am I? It'll be fine!