Why would he do this when he knows what I went thru w/my ex?

About 12 to 13 years ago this guy had a crush on me when we were in school. I was w/this other guy though who I ended up marrying. We were married 7 years & just recently got divorced. Like 2 weeks after our divorce was final I ran into the guy that had liked me years ago & we've been talking ever since...he says we ran into each other for a reason. My ex & him knew each other...they weren't close friends...but they hung around some of the same people so they were cool w/each other. Anyway, I am attracted to this guy too but he's not looking to be serious right now. We've hooked up a couple times. He wants to be fwb first so we can be careful & take it slow. I don't want just casual . We had a talk the other day about what to do & he says he has feelings for me but he hasn't been calling as much as before & now I just feel like he doesn't like me as much. Why would he put me thru this when he knows what I just got out of(my husband cheated) Why would he hurt me also?