Ideally, if you are with the right person and comfortable with each other, you shouldn't have this problem, because you would be comfortable saying "no". Another test -- are you comfortable passing gas in front of this person? It sounds funny, but it's a serious test of how close you are and comfortable with each other. You shouldn't have to pretend to be someone you are not with that person. It's one thing to be courteous or considerate, but it's another to be a bundle of nerves, anxious that you not offend them. To me, this is a relationship that shouldn't go very far, if you both want to be happy.
I do, however, remember being in relationships like this. It was my very first one, where my self-esteem and confidence was very low, and where the person I was with wasn't a perfect match. I was way too worried about her all the time, because I felt like I wasn't a very valued person by my peers, so I was "lucky to even have someone." Also, I see this in the first stages of some relationships, where two people are still seeing if they like each other. This stage shouldn't go on more than like 4-6 weeks, if even that. If it goes longer, maybe you both need to open up and see what you are both really like.