Guy's Behavior

Why does he ask about open relationships or breaking up in minor inconveniences?

As stated, when he is feeling a bit worried about the relationship or when we get into arguments, he'll ask whether I want to break up or want an open relationship. I am starting to think that he is either wanting to see other women, or that maybe he has cheated and wanted to use it as an excuse. I don't want to 100% think that just yet because I could be getting ahead of myself, but it is causing me not to trust him and it is pushing me away. He also has a tendency to say, "well this girl asked me out today" if we get into an argument. I will speak to him about it sometime this week to get an understanding of him and to tell him it needs to stop or I'll have to walk away. For me, it is either that we are together or not. No one else should be brought into our relationship. Of course girls will hit him up, the same way guys have still been hitting me up, but I take no notice in it as I am devoted to this man. So guys or women, help me out please? Why is he doing this? It gets me really upset. You can be brutally honest and say he doesn't love me etc. As I said I will speak to him about it when we have the chance to meet up, but does anyone understand his mentality and why he is doing this?
Why does he ask about open relationships or breaking up in minor inconveniences?
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