Me vs. Ex shit gone wrong.

So my guy, who I have been talking to for about 6 months now. Just called me and woke me from my sleep to tell me he called his ex fiancée and asked her to come over. And she did. He promised me nothing happened etc. and he only wants to be with me, etc. but the thought of it all makes me so uneasy. They obviously have history. He called her for a reason and she answered for a reason... and she CAME OVER for a reason. Otherwise she wouldn't have even answered the call when his number or name popped up on her screen right? I told him over and over that I refuse to compete with anyone FOR anyone. Am I wrong? What should I do? I told him we would speak about this at a more suitable hour...  which means in the morning. So girls.... HELP.