I loved A but he left me i met R?

When i met A i fell head over heels in love with him but he left me after 4months. Was hurt but eventually got over it and moved on begun dating meeting R . 15 months later A reappeared back in my life. I stopped my seeing R and we picked up our relationship where we left off.We are engaged but R keeps calling. i chalk it all up to bad timing cause had the ex not came back i would be with R. confused who to chose.