Hi kelzie - first off, you sound like a great mum 
It is such a tricky situation and there is no right answer, all you can do is what you feel is best for your daughter.
I was never close to my mom when I was growing up, I had lots of boyfriends between the ages of 12-14 but sex and relationships was never really discussed. When I was 15 I got my first 'real boyfriend' who I did love and it was him I lost my virginity to. Even though I was at that age my mom still didn't talk to me about sex/contraception and I fell pregnant 3 months after meeting him. We had waited until I was 16 to have sex though. I'm not saying my lack of closeness with my mother was why I got pregnant (I was also young and stupid, I knew what I was doing) but I often wonder if things would have been different if I felt like I could talk to her about that side of life and her her advice and support. Needless to say she ended my relationship with that guy and the topic was never spoken about again.
As I progressed through my teens I continued to have boyfriends and despite me having fell pregnant previously my mom still didn't sit down and talk to me about the responsibilities of sexual relationships and contraception etc - though she would make occasional references to "to trouble I once caused" 
I was never, ever, ever allowed a boyfriend to stay the night. I wasn't even allowed them in my bedroom, even though I had a downstairs bedroom which was next to the living room. Even when I was 19/20 boys in the bedroom was still a definite no-no. I knew better than to even ask if my boyfriend could stay over. My sister was slightly older than me and even when she was 21 and had been with her boyfriend for over 2 years, he still wasn't allowed to sleep over. I think the first time I ever had a boyfriend stay over at her house was when I was about 23/24 and I had gone to visit her for the weekend as I had moved away to Uni by this point. However, from the age of 17/18 she'd had no qualms about letting me or my sister stating at our boyfriends houses, they just weren't allowed to stay with us at her house.
I'm not really going to pass any judgement on your situation as I can see both sides of the argument - I just don't think it is as black and white as some people want it to be. I think the most important thing is to keep things open and honest with your daughter and do what you think works best for you as a family. Your daughter obviously trusts you and feels close to you so you are definitely doing something right. I would have loved to have the kind of relationship with my mom that you have with your daughter x x