My boyfriend wont have sex with me any more...what should I do?

ive been going out with my boyfriend for just over a year, I am 29 and he is 28...at the start and for at least the first half of it we used to have sex a lot, we have always been very attracted to each other. However we did move in together very quickly. Over recent months, ive noticed he has wanted sex less and less, whereas I have a very high sex drive. It got to the point where he would never touch me but i had to initiate it every time, and most of those times he would make up some excuse not to do it..(usually that he is too tired). Recently we had to be separated for 2 months for work reasons. The problem is, since we reunited, the sex life is almost non-existent. In the 2 months apart I couldn