Relationship advice needed please help!:(

Hi I'd like some advice what would you all do if you've been with someone for over a year things seemed pretty serious but you just fell out of love with them and now everything they do irritates you your argue with them all the time but they still love you to pieces like it would end there world if you left them you're the only person they feel like they have in life but pretending to love them back is hurting you, I still care about them so much they were my first love but it's hurting you so much to be with them? Please give me advice I have no one to turn to as my family love them and don't know about any of this? Xx