Sounds like you're on your way...
Hi Ms. Beachcutiegirl,
Good to hear from you again. Congratulations for successfully transforming your previously-conventional boyfriend to your cuckold fiance!
beachcutiegirl said:
I decided I couldn't stop being with Cameron, I became addicted to his cock and needed him to dominate me.
Hey, there's nothing wrong with that. If Cameron's dominant personality and cock are what you need, then... well... that's what you need.
beachcutiegirl said:
It got to the point where I didn't care if Lance and I stayed together or not; I still loved him but wasn't willing to give up the feelings I got with Cameron.
Earlier I would have suggested it probably wouldn't be necessary to give up your relationship with Lance while continuing to fuck Cameron, but I see that question has become irrelevant...
beachcutiegirl said:
One night after a fantastic dinner Lance and I were at home having a wild fucking session when I brought up the idea of him watching me with another guy. He looked real surprised .... but I wouldn't let him stop. I kept riding him while asking if he still wanted it.
You have good intuition; that was the right way to do it especially if you were fucking Lance with him in a male-inferior position — i.e., riding him, as you say, with you on top.
beachcutiegirl said:
I think the heat of the moment got to him because his shock turned into raw passion as he fucked me harder than he ever has, smacking my ass and yelling how he wanted to watch me get used.
That sounds like good psychological talent, posing your question and extracting an answer from Lance while he was in the heat of passion but before he had orgasmed...
beachcutiegirl said:
I got caught up in the moment and just screamed that I already was, I spilled everything to him. I told him how I had been going behind his back while he was at school and work and that I had been getting used at least once a week by Cameron.
Oops... that was risky. But, as I mentioned above, such considerations are now irrelevant.
beachcutiegirl said:
He came instantly and both fell down in our bed, overwhlemed with what had happened.
Obviously that was Lance's answer. You couldn't have hoped for a better reply...
beachcutiegirl said:
After the moment wore off, Lance asked if all of that was real. I felt ashamed but admitted that it was. He looked destroyed and betrayed and took it pretty hard.
But, he realized he had already told you, in a way you couldn't mistake, that he was strongly turned on by you fucking another man...
beachcutiegirl said:
After getting over the initial shock that it had become a reality we were able to talk about it. I explained my need to be dominated and that his fantasy of watching me get used only made me want it more, and that I understood if he didn't want to be together anymore. He left for a few hours to go collect his thoughts and when he came back home decided that he wanted it to keep happening, as long as he got to watch.
Your gamble in the heat of passion paid off, and your winnings were as large as you had hoped...
beachcutiegirl said:
We came to an agreement and the next time I saw cameron I let him know what had happened. We all met up one day a month or two ago and worked out our boundaries. Now I get used and abused by Cameron about once a week while Lance watches and takes pictures of us or jacks off.
Excellent. Clearly you're very skilled, Ms. Beachcutiegirl, at guiding your men to where you want them by exploiting their sexual cravings...
beachcutiegirl said:
[Lance] hasn't gotten to have sex with me since we started all this.

Hm... you might begin considering how to re-establish some form of relationship with Lance, not necessarily the same as previously, that will strongly appeal to his sexuality — so he doesn't become bored and increasingly frustrated with you having another lover, and begin wondering what's in it for him and re-thinking whether a continued relationship with you is a good idea.
If you have in mind your "cuckold boyfriend / hot fiance" relationship transitioning into a successful and continuing "cuckold husband / hotwife" marriage, you might consider the desirability of establishing yourself as dominant partner and Lance as your submissive fiance, such that the hierarchy is: Cameron (as your dominant lover), you (as submissive to Cameron [which you find sexually appealing] but dominant with respect to Lance), and Lance as your submissive cuckold fiance.
To a certain extent, this seems to be your situation now vis-a-vis Cameron and Lance. But, you might give some thought to whether it would be desirable to make it more definite. For example, you might consider informing Lance that you will allow him sex with you but only if he will consent to first being put in bondage by you.
See (for instance):
Sexual Power for Women, by Georgann Cross:
Sexual Power for Women
Lady Misato: Real Women Don’t Do Housework:
Real Women Don't Do Housework
Queening your man:
The Fine Art of Queening
Musings of an incidental hotwife (and other links):
Musings of an incidental Hotwife: Why he doesn’t want other women & how to KEEP it that way
How to bend over your boyfriend and make him like it:
How to Bend Over Your Boyfriend and Make Him Like It Sex Secrets
and the DVD (readily available online): "Bend Over Boyfriend."
beachcutiegirl said:
Sorry for the choppyness of this post. So much has happened that it's hard to put it all into words.
Your post is not "choppy" at all. You're a good writer... and, I would guess, verbally articulate as well.
beachcutiegirl said:
I love this new situation, though, and hope I can keep making my fiance watch me in these situations.

Good! You have successfully guided your fiance to the right track. And, congratulations on your pending marriage! (I gather that too is a new development since you initiated this thread.)
—Custer