Monogamy - as outdated as wood?

So, as you may have gathered, I have come to the realisation that I need to grow up and stop leaning on men for support.  That scares me, as I wrote something very similar 8 years ago.  I know I have grown up a bit, but I'm scared I'm still the same person.  IS it possible for personal development to stop for 8 years, when you're NOT addicted to drugs? And I'm annoyed with myself for how often I use 'but' in my writing; poor English skills Phoenix!
Not having a break from men for 10 years essentially means I have been in the same relationship for 10 years. No wonder my growth has stagnated.   The guys have been interchangeable, but have I ever respected their differences and treated them as individuals, instead of just seeing them as 'they guy I am involved with'?

What I really find myself wondering tonight is, will I ever find a man who gives me everything I need, or am I destined to always want more than 1 person at a time?  I don't believe in monogamy, but I do it because that's what the guy usually wants.  A few times I have slipped, but I have tried to hide it from them to protect their feelings.  It's not about lying, I'd love to admit to wanting an open relationship, but as many men know, saying that out loud is so hurtful to the person who only wants you.  It doesn't mean you want them any less, its just saying you want to have freedom to engage with others.  I wouldn't be hurt if I was told this, I'd applaud it - and possibly participate depending on how hot she was and if she was up for it (of course).  But as I have discovered, there seems to be an unfortunate correlation between longevity of relationship and frequency of lovemaking.  Maybe I get unsexier the longer I'm in a relationship, maybe they get more comfortable with me - but I need it often or I get bored.  At least I have the courage of conviction to admit that.  It may not be a classy thing to admit to, and it may not be socially acceptable, but I am being honest (and blogging under a username to keep things anonymous).
But my fundamental question is - What's wrong with seeking different things from different people? Maybe that's healthier - if we have more than one platonic friend, who we accept the flaws of, and friends to do different activities with, why do we expect one partner to encompass it all? Maybe we should try to be happy and stop waiting to be saved.  Or maybe we should be more open-minded to the idea of multiple partners.  Long as everyone uses condoms and respects one another, whats the problem with open relationships?

Perhaps I should have been born in the Sixties