If he'd missed you as badly as he says he does, why did it take you to be the one who made the first move and after all this time? Surely he'd have made some effort to contact you? IMO you wouldn't have been the one to have made the first move, he'd have done it. When a guy still has feelings for a woman, he would move mountains in his quest to win her/woo her back..when a guy has feelings/love for a woman, it is impossible for him to ignore that pull towards her - he wouldn't have kept away for so long.
Sounds to me and this may seem a bit harsh, but in your contacting him, he's seen what he views as an opportunity for 'sex with the ex' and so he's giving you the bull * * * * lines that he misses you, still thinks of you, etc. Of course he's gonna say all that, he's trying to sweeten you up - he's after 'sex'.
Not saying that he may not still have feelings for you, but the fact that he mentioned 'sex' almost immediatley after your contact, is a huge indicator that this is what and all he has on his mind with you.
Now he's ignoring you because he hasn't/isn't getting what he wants from you. He's seen a change in you, you are acting not so 'besotted' with him anymore, he knows he aint gonna get the sex as easily as he assumed he would. He knows it's gonna take more than a few sweet words on his part to get what he wants from you - and it's too much like hard work for him, so he's backed off. He aint interested in you as a partner anymore, but as in a bedmate, else he'd be prepared to do the work involved in winning you back!!
IMO he aint worth your time, find someone else who is, he's out there somewhere.
Good Luck