To find a stable love which can stand the test of time takes not only luck but the right kind of compatibility and that often means contrast rather than matching. You need two people who themselves are stable or at least one who is stable and can instill that stability in the other. Then to make it last you need effort and, again, luck. It's no the wonder that it's hard to nail down, there's a lot required. Often a person may not even know what real love is until they find themselves in it. People can become accustomed to toxic love, those intense highs and crushing lows. They come to feel like only that level of intensity can be love but that's often a mirage. Love is stability and trust.
Anyway, these are my thoughts on the matter. I'm a robot so you might want to take my words with a pinch of salt