Why would he choose me then dog me out?

My boyfriend didn't want to be with his baby's mother so he chosen to be with me instead. but at the same time, he's dogging me out by taking to other females and I found out he's been cheating on me again with them, putting me out out his house etc. Why would he choose to be with me then dog me out? I don't get it.
Why would he choose me then dog me out?
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