So basically I'm very interested in this person(let's call him person Q) and I asked my friend if person Q has ever said anything about me..My friend smiled and said that person Q said I was cute. Of course I got super happy and started asking dumb questions like "oh when did person Q say this" and "oh how did person Q say this". My friend said that person Q is a good person, but mentioned he was a man whore in the past but isn't anymore. My excitement quickly faded and I said it would be hard to trust him and I basically said I shouldn't get to know person Q better and I should give up on person Q. My friend said it sounded like I was insecure; he didn't mean for it to sound hurtful, but it really got me thinking of what he said.
About 10 months ago I was in a "friends with benefits" ordeal with this other dude. We only saw each other once a week and it honestly drove me insane. I was always worried if he was seeing other girls and I honestly just wanted to get to know him better such as what he did in his personal life and such ordeals; this never happened due to the little time we actually spent together. I found out during the time we were "together" he had a girlfriend, I also found out in the past he slept with over 40 women... It honestly broke my heart, and the whole relationship was toxic. During the whole time I always felt uneasy and always has questions running through my head, I hardly asked him anything because I knew we where only friends with benefits despite the fact I actually really liked him. 
I always thought being insecure meant not feeling good about your body, but now I realize through my experience you can be insecure about an ACTUAL relationship. To sum it up I was extremely insecure about my whole "friends with benefits" ordeal and I feel the pain I went through is going to effect others relationships I may be interested in.

I would love if you could give me your personal insight on the whole situation and explain what I should do with myself. I would love to hear personal experience stories and it would be super cool if someone could explain to me more about what insecurity means.