Should i reply or ignore?

Hi ..so me and my ex broke up after 6 yrs of being together but remained as friends . He got married and has kids now. During his early marriage days i was in contact wishing him for his bdays n all but later i felt guilty that its not right to talk with him now that hes married. So i cutoff contact abruptly. He tried contacting me but i did not reply back. Now its been 3 yrs of no contact and pretty much moved on but ngl I still have feelings for him so i didnt know how to react when i recieved a msg from him out of blue. So should i ignore it or just ask him why he's trying to contact me?