1. Your analogy sucks and you appear misinformed on how conferences add member schools. The total SEC members schools are set by the CEOs of the SEC (one from each school), and then a 75% vote is required to formally extend membership to any other school. On your analogy, I only had to convince my hot wife to marry me, not 75% of her friends/family/sorority.
2. UM was never formally invited to the SEC, but I understand your historical reference point. I assume you are talking about 1990, when the SEC voted to authorize expansion. At that time the SEC identified six schools as "potential" members: Texas, Texas A&M, Forfeit State, Miami, South Carolina and Arkansas. Arkansas was the top target because they wanted to raid the SWC, and not surprisingly they were the first team in that summer. That left 1 spot open. The Texas schools were threatened by the state legislature with retaliation if they left (because it would kill the SWC), so they backed off. F$U was the next school, but they ****ed off the SEC by flirting with the ACC. That left USC(e) and UM. USC(e) had a preemptive vote (before a formal membership was ever extended) approving membership. At that point, Miami went for the Big East (allegedly to help our basketball program, of all things), USC(e) joined the SEC, and the rest is history. Miami was apparently choice five of six, but based on the circumstances UM probably could have joined the SEC at the time.
That said, this all happened over 30 years ago and it is pretty irrelevant to whether UM could join the SEC today. A lot has changed.
3. About 10 years ago when the SEC expanded to 14 schools, Georgia, South Carolina, Florida, and Kentucky absolutely formed a blockade to any school from their respective state being offered membership. And they were vocal about it. Because of the 75% majority rule for voting in new members, those 4 members were effectively able to defeat any vote to bring in UM, F$U, GT, and Clemson. As a result, TAMU and Missouri were brought in. Although there are now 14 teams, the rumor around the SEC is that TAMU has aligned itself with the Georgia, South Carolina, Florida, and Kentucky "blockade" in order to keep UT (especially) and other Texas schools from ever joining the SEC (not that it even matters, because those 4 schools alone are enough to block UM). In other words, UM isn't getting in now for political reasons.
4. As far as $$$ is concerned and the SEC needing UM more than UM needs them, the SEC is the most profitable conference in all of collegiate sports. Meanwhile, the ACC's revenue distribution per school was even less than the PAC-12. The SEC may someday expand beyond 14 schools, but it likely will be of a greater financial benefit to the schools joining than to the conference itself.