How can i tell when someone looses interest in you!?

ok so im so in love with my boyfriend and we've been dating for about three years. we started out as friends and we talked every single day. when we started dating everything was great and really still is. we can talk about almost everything and i love that about him.but in the winter he is very active with his skiing career and really doesnt have as much time for me. i usually go wtih him when i can, but when i dont go with him i usually go without talking to him for up to a week. i hate it so much. i dont like to be needy or annoying so usually i wil just send a cute text message or an im telling him that i miss him and love him. just the other day though i was talking on the phone with him and he started talking about this girl his friend and how much he likes her. i really dont know what to do about. he tells me that he loves me and me only but i do have doubts sumtimes. this is the same girl that when we were just friends he had been talking to which was awhile ago. i asked him in a nice way if he wanted to just be friend again( which i really dont want) and he simply responded that we would talk about that later. and 2 weeks later have yet too! now everytime that i want to talk on the phone with him hes too tired and just wants to go to sleep or talk online. i really dont know if hes getting sick of me? or am i just over reacting to the situation? help me?