Situation unknown

Me (male) and my friend (female) know each other for over a year now. We study at the same university, same major. At the beggining of our relationship i thought that we may be together, though my friend told that she wanted to detach a bit after two unsuccessful relationships with her previous boyfriends. Now, as we started to meet more often (not only in group, but we spend some time 1 on 1) i consider becoming a couple. Based on her reactions I know that she really likes to spend time with me, talk to me, she feels comofortable with me, but she is somehow avoiding physical contact. Of course there is no holding hands, and kissing, but she's not even hugging me on farewell. But she allows me for example, to play with her hair. I am a bit confused. I am afraid that telling her that i want something more than just a friendship can ruin everything including friendship. I don't want to lose her even as friend. Meanwhile, me and her have someone on the side, but nothing huge will be coming out of this, probably. Should i just wait and see how the situation between us is going, or should i just go straight with telling her what i feel?