What makes a relationship a relationship?

I thought it was about time to make a post although I'm not very good at getting my point across, be warned!

My girlfriend and I have been together for four and a half years. Although things were great in the beginning things have cooled down alot over the past couple of years and I can't help but feel that we are closer to flatmates than 'in a relationship'.

We moved house a year ago but she made it clear that she didn't want to buy a house with me but wouldn't give me a reason. I bought the house and she pays me each month for bills and stuff.
We sleep in the same bed but I have regularly shared a bed with people before.
Sex is a big issue. We have sex once every two or three months because thats all she wants/needs. When we do have sex it's straight forward sex, she won't go down on me and rarely lets me go down on her and my hands aren't allowed to go below her waist. She knows I'm very unhappy with that but I won't pressure her.
We say 'I love you' all the time but I say that to my family and some close friends too.
I like to talk about the future of a relationship sometimes but all she will tell me is that you never know what is going to happen.
When I look to the future I can't really see her as a mother or as a wife. She doesn't like to talk about any of that either.

So am I really in a relationship or am I just very close to the person that I live with?

Judging by your post I think you already know the answer to your question. The real question is 'what are you going to do about it?'

It is very obvious to me that if a romantic spark ever existed between you both that it has long since been extinguished, and been replaced with familiar routine. There is nothing wrong with being good friends, but you have to ask yourself if you want more than that. If so, it's time to end the relationship and look elsewhere, because it sounds like neither one of you wants to be together for the long term.

If that were true, I'd still be here.

Oh, you're in a relationship alright. The question is, is this the kind of relationship in which you want to invest more time. Were I in your shoes, I'd end this one now.