How to define the relationship??

I've been with my boyfriend for just over 6 months. When we fist started going out, we said we weren't looking for a relationship (which at the beginning we really weren't!) But I feel like in recent months it's become more relationship-y. It's not focused just on sex anymore, we talk more. I feel more connected to him and I have real feelings for him. He came to visit me over Christmas because I wasn't feeling well. But I don't know if he feels the same way. How do I bring up the talk to seeing he feels the same way and define the relationship? I'm terrified he'll just end it. I really like him and I'd do anything for him. Any advice on how to gently bring it up?