My boyfriend getting back with his ex

So me and my boyfriend been dating for a few months and he already told me he was with someone for 3 years and was engaged to her for a month but she broke up with him. He moved over here to a different state and that’s how we met he told me he still loved her but he’s slowly getting over it. Now he’s going back to his home time for a wedding and she lives there too and he said that she wants to talk to him when he get there. Now he said he thinks that will break us up and I said do you want to hook up with her and he just said they are going to talk. I said are we still together and he said he thinks about her and he doesn’t know. Like wtf why?