I Really Like Her But I Am Unsure of My Sexual Feelings

Recently I have began spending a lot of time with this girl. We've known each other for several years and she has never hidden it that she was attracted to me although she hadn't really made any considerable attempts at pursuing anything more than a flirtationship. Well start about a month ago I began spending time with her alone at her place and I have an amazing time with her. I'm so intellectually and emotionally attracted to her it's insane. The problem is she's a bigger stud. In the past I've only been with girl my size or slightly heavier but she has quite a bit on me weight wise. We have messed around and with her being the more dominant out of the two of us has initiated sex where I was on the receiving end But I don't feel comfortable at all returning the favor because 1. I'm not even sure if she is into that. I'm pretty sure she had never received and could possibly be a touch me not stud. 2. She is bigger than me and I don't know if I am physically attracted to her to that extent. How do I approach / handle my dilema. She is the biggest sweetheart and I really really like her. I love giving sexual pleasure to the girl I like But idk if I'm ready for this step yet. What do I do?!?!:help: