I need advise, please.

So, I've been in love with my boyfriend for 3 years, and we finally started dating in October. (We'll refer to him as "L")Things are absolutely wonderful and he makes me so happy. But unfortunately about 2 years ago, I started dating a different guy, we'll refer to him as "C". The only reason I ever dated C was because I was trying to get over L because I thought L was giving me the go around. I ended up losing my virginity to C and we broke up 3 months later, because he wanted to be with a different girl. Now that I'm finally with L and very happy, C decided to come back into my life after he was with the other girl for over a year. He claims that they broke up and he's wanted to end it for a while and he wanted to get ahold of me months ago because he misses me and realizes he fucked up by leaving me in the first place. I don't believe anything he says because of how he treated me. He took everything I had and ran with it and has only now decided to come back because he knows I'm happy.

So, my question is, how the hell do I get him (C) to leave me alone without him starting stuff with me and L? I love L more than anything and I don't want to lose him or any of his trust because of C.

The first picture is me and C

(I only have it because he sent it to me yesterday while whining about wanting me back)

The second one is me and L.

Thank you for any responses.