Can a guy truly be JUST friends with his ex?

My boyfriend was in a 7 year relationship (I divorced from a 12 year marriage) and he still talks to his ex daily. It didn't start out like this but I have expressed it makes me uncomfortable. He says he isn't one to throw people away and she has "no one else" yet she's engaged and pregnant with another man's child. My boyfriend says I need to trust him or it's going to hold us back from growing as a couple. My ex husband cheated on me so yes, I have trust issues and he knows this... is it too much to ask that he alter the parameters of the frequency in which they talk? I don't care if they are friends, I still check in with my ex on occasion so I get it. I hate feeling so scared and guarded all the time. I want to feel safe and I don't.
Can a guy truly be JUST friends with his ex?
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