help me i need advice

l • 3/11/20 my wonderful bf

i dont know what to do cause im dating this one guy and he seems obsessed cause every few minutes he wants to call and he asks me what im doing and he is going to fast but i have started missing my ex that i thought cheated on me but never did and he misses me too and still loves me and i feel the same way and i want to be with him so bad but i dont want to break my bf’s heart idk what to do please help