Sex an consent

My boyfriend and I only see eachother on the weekends for various reasons but whenever I go there to stay the night the first thing he always wants is to have sex even if I tell him that I don't want it that I'm not in the mood he will continually ask and beg, or try to play with me or even start jerking off beside me....

How can I get him to respect me and take no for a answer...

Edit.. We have been together for two years and don't get me wrong I love to have sex but somedays I just want to be cuddled and feel like I'm loved... I feel so miserable because it feels like sex is all he wants