No. I've always owned a horse or pony, though--I was raised around them--so it was never a "big decision" to buy one. I just always had one, so I would have had to make the decision to sell in order to not have one, if that makes sense.
There are days when I think how much simpler my life would be without one--for instance, the extra money I'd save each month (I'm unmarried with a full time job; I would have enough money to buy any car I wanted and/or do all kinds of fun stuff, but instead I budget every last penny to be able to afford my horse and various shows). There are days when I really just don't want to ride and am less than thrilled about the fact that I need to, since my horse is my responsibility and if I don't do it, no one will.
However, he's also there when I need an escape from everything else. There are more days (especially when the weather is good :)) where I'm grateful to have him than there are days that I'm not. I love showing and every horse show reminds me of how much fun I have doing this sport.
Now that I board, it helps--because he's cared for no matter what, so I don't have to give up other activities just to make sure I'm out there twice a day every day or at certain times. I still try to go daily to ride, but if I want to make other plans, I can. It's hard when you are forced to choose between owning a horse or doing things every other person your age is doing, because if you miss out on every activity that your friends do, you'll have a lonely life. Figure out a compromise. Maybe you can board your horse, so that every now and then you can take a day off from riding/horse stuff. If you keep him at home, consider your arrangements. I kept my horses at home all through school, but they were on 24/7 turnout and it was a family thing so it wasn't like I had to be there all the time, every day. That definitely made it easier.
Anytime you have something that takes up a lot of time or money, you'll have moments where you think of what things would be like without it. That doesn't mean you shouldn't do it--just plan it so that you aren't burdened so much that it becomes something you hate. It's like the people who decide they love horses so they want to make it their job--and they end up hating it because they can't get away from it and it's not fun anymore.
So yes, there have been days when I wished I didn't need to go ride because I really wanted to do something else, or days when I worried about money and knew that I wouldn't be worried about it if I wasn't trying to support a horse, but there are more days when I'm thrilled to have him and I know that I need that in my life. That's what makes me happy. It has to be balanced out with other things--I have a full time job, a serious boyfriend, etc.--but when I can't go ride for a longer period of time for whatever reason, I am much more stressed or unhappy. I don't regret having my horse or spending money on him.