I agree, I also have a one year old who is a nightmare when he hasn't had enough sleep, when he has he's a dream. Things to look out for with kids who are tired is irritability, not seeming to know what they want, frustration rather than genuine upset, and common tantrums. You haven't spoiled him, you've loved him.
As a guide, it seems most kids who are overall relaxed have 12h straight at night and 2h sleep after lunch. Does your do that and if not how far away from it is he?
If anything rather than spoiling, it may be that you going to him at night has become a habit. Is he waking looking for comfort or is he hungry? A big bottle of milk at night helps here, but they also need to be getting enough calories in the day.
To get a good daytime pattern going, make sure you get outside in the morning. Go to a class, the playground, anywhere he can run around and be happy then straight back for lunch and to bed. Don't let him get overtired otherwise it makes things worse. Even if you have to give lunch at 11-11.30 finding that right window to get him a good sleep in the day really helps.
Sorry if you've tried all this or it's totally irrelevant, good luck, it's not your fault!! xxx