He can like someone else?

Oké, so a while back my boyfriend told me he was feeling things for an other girl. After a while he realised it wasn't gonna be anything and told me all of this. I was sad and everything but we stayed together cause he said this made him realise he really needed want wanted me me.
We were talking about this and he told me that for him it is always possible to fall for an other girl, that there is always the possibility that he falls in love with someone else cause he can't help it. What the hell does this mean.
He can like someone else?
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