I wonder who would enter a relationship build on these foundations?
Can you explain why you think "loosing your partner" is bound to happen when they have sex with other people?
What about them falling in love with a co-worker (no sex required), dying from a car accident one day etc.?
How do you assume these things are less likely than when sex enters the picture?
Your emphasis on sex and what meaning it carries in relationships (particularly successful ones) seems to be be completely disproportionate to reality.
People in open relationships tend to give more assurance to each other.
Jealousy always exists. I can be jealous because my partner goes to her "girls night" and I don't get to spend time with her.
Why would I be more or less jealous than if she had a date that night that involved sex?
Once you think about this for a bit you realize that the choice/reasons for jealousy are mostly arbitrary/cultural and can be overcome. Like any bad habit.
As for access to sex: there are options for men to balance the sheet. Just take up some sort of social dancing; tango, swing, salsa etc. Or sport. Climbing gyms are playgrounds for singles.
And these options also open the door for "having sex with a stranger/recent aquaintance tonight".
If that is so important to you.