<human>: Condense the text into a few key points

So I've never been in a situation where my S.O. is still close friends with his last attraction. He mentioned that he was crushing on her for 3 years but he is now over her. He said he didn't feel anything when he saw her with another guy about 2 years ago and he mentioned that he liked other girls in those 3 years from time to time too.
They talk online sometimes and although he tells me that he loves me I can't help but feeling a bit insecure. I think the worst fear for me is that he still likes her and it becoming obvious to me. It will hurt so much, and I am hesitant about being in a relationship with a guy who still has feelings for other person. I talked to him about this and he said I have no reason to worry and told me he doesn't have any feelings for her at all. 
I guess what I'm asking here is, is my fear irrational? Is it possible for someone to completely get over their crush and become close friends (and not have any feelings)?
<bot>: Boyfriend is still close friends with his crush of 3 years and talking every other day. Feeling insecure. Is my fear irrational? What can I do to help?