Wondering

I dont like feeling this way, knowing it's me he'll betray. He loves her and claims to love me, loving 2 can never be,only one ends up truly happy and it ain't gonna be me. Never did I think i'de grow to love him this fast,but I always kept in mind that we wouldnt last.He refused to let her become his past. When he called her,I should've walked away,but my big heart made me stay,knowing he'd break my heart some day. He wants me to show him love and affection, why?when she has all of his attention. I dont know what to do;walk or stay,all I can do is pray.Should I stay and keep my cool? or leave before I become the fool. Will he be like the rest and pull my heart right out my chest.