life with GF. Affecting relationship?

Hello all. Have been with GF for 1 1/2 years. I love her. We get on great. Only problem is our life. We have maybe once per week. It is fairly pedestrian. I know she had very active lives with her ex's - tapes, rough etc. I guess i am jealous of this. She tells me lots of reasons why we dont have sex - no time (we work a lot), she feels fat lately, i am not good at turning her on, her last bf was abusive etc etc. We have spoken about marriage lately. I love her but the sex thing is holding me back - I just wish there was more sex between us. Is it resonable for me to ask her to make more of an effort at sex - to make time for us? Is it reasonable for me to explain that our sex life is holding us back from moving forward? Thanks. W