How can I get a guy to put his arm around me?

Sorry about that a-holes earlier answer. Look man all you do is just do it when the time is right. Decide when your gonna do it and commit, just GENTLY AND SLOWLY place your arm around her like youre a crane lowering an atomic bomb that is unstable and youll be there. If she is going out with you then she knows it could happen and that means she probably is looking forward to it

in my opinion which is a girl's opinion do what he says but also know if she really likes you she will either touch your hand or put her head on your arm

if she looks at you for a long time and gives you waiting eyes go in for a kiss.. that is probably what she wants. good luck!! also remember girls like romantic moments so be sweet and gentle if she pushes you with urgency that is you signal to step it up a notch.