Why would my boyfriend break up with me and then lie about liking another girl in our relationship and then says he loves me and all?

so basically about a couple months ago my boyfriend broke up with me and then i later found out that day that he liked one of my ex friends who at the time i wasn't really friends with.

i even had proof and all about him liking her during our relationship he goes and lies about not liking her or her even talking to her at all.

i just dont get it i mean we started talking again we were dating for about almost a year when we broke up and we only broke up for about a month and now were together again but i just dont get it.

Why would my boyfriend break up with me and then lie about liking another girl in our relationship and then says he loves me and all?
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