Guys, why play with a girls heart so much?

My ex and i dated for about 3 months and i love him and trusted him so i lost my virginity to him. He just seemed like that perfect person. Then he randomly couldnt do the whole relationship thing and wanted fwb i felt like i was being stabbed in the heart. I just trusted him so much! I then find out he is now back together with his ex who he was with for 2 years but dated years ago. This hurt but i decided i didnt need him and had to to move. I did the whole no contact thing, deleted him off facebook and phone. He contacted me a few times to see how i was doing then he calls me a few nights ago being tipsy and admits he misses everything about me, hanging out with me, my voice. Why is he doing all this while hes still dating her. His girlfriend is also long distance she doesnt live her. Why is he playing with my heart like this? Does he truly miss me or is he going through a rough patch with her and is using me