What would you do in this situation? Would you move in or not?

I have been seeing a guy now for 7 months. It has been rocky sense it started. I now says he loves me, and I have had feeling towards love for him but they have been knocked back because of another woman. He is a sweet heart that is for sure, but I do not know if he is just that way with me. When I started dating him I knew he had a good friend that was a girl. He had her move in with him, because of some financial problems right around when we started dating, because I said no it was too soon. It started out to where it was all okay for us to be in the same room, and then things changed. Now everytime I would walk in a room this girl friend of his would roll her eyes and huff and puff. This really upsets me because we have never had a falling out and this girl is close to his family too! One night I can over to his place and he told me to go into his bathroom and look at the underware of the female he had cheated on me with. I just laughed it off...did not even go in the bathroom. Once I did I found underware in the bathroom and they were not mine...he said he though they were mine! Then he said they must be his friend's. Well she is too much of a ***** for me to ask her so I just got upset cooled down and took his word for it. Then a couple of weeks later I woke up and he said her name in his sleep. I mean this is horrible! He said she was moving out, because her and I do not get along. He wants me to move in with him at the end of this month. I am torn! I do not know what to do. I really like the guy think he could be a great man for me, but I do not know if he is being sincere. He is in Cancun right now with...his brother, mom, and her! They had this planned out for awhile now and even asked me to go, but I could not go because of her. What would you do?