Anyone Have Relationship Advice for Me?

My boyfriend and I moved in together in September. Everything was fine up until New Years. Lately he's been really distant, and reserved around me. We used to talk about everything, now he just clams up when I walk in the room. He still acts the same around his guy friends from what I can tell.

I've tried talking to him about this and all he says is "it's stress". Understandable, but he won't tell me whats stressing him.

Even our sex life has taken a significant hit. He hasn't touched me since December, and whenever I make an offer, he says "it's not you, it's me, just not in the mood."

Am I reading too much into this? Or should I just take a back seat and let him work whatever it is out?

Any help would be awesome.

Thanks in advance and sorry so long.