Could there be someting going on?

been in a relationship with this great guy for a year . we used to go out and have a good time all the time now that we have moved in with each other he ha become a home body when he leaves hes not gone long n he tells me weres hes going ,, but 4 the last couple of months hes been acting weird while hes at work he wont answer some of my texs or ?'s acts like he doesnt want botherd all he talks about is work n this female co worker that hes ben working with 4 over 9 months and here to find out the people at his work dont even know about me .. he says he dont talk about his person life but he tells me about theres all the time we never have anymore he tells me nothings going on but why is he different having fun with them n acts like a couch potato at home and makes me feel he wants nothing to do with me im just worried something might be going on at work with this person why hes different with them/her then he is with me .. now his job is working with 2 mentally changelled guys .. i