If you had two successful startups, maybe chances are that you don't put much time into other activities which includes dating and the relationships that can come from dating?

If I said I was going to try to have a successful startup putting a couple hours a week into it now and then, what is the probability of success? So maybe the issue is going up a learning curve?

If you do eventually find yourself in a relationship, here is some advice for making it work from Emma McAdam and also the Gottmans:
https://courses.therapyinanutshell.com/relationship-skills
https://www.gottman.com/couples/workshops/art-science-of-lov...

The Gottmans also supply dating advice you can sign up for on their website, but I don't know what it is. I would guess though it is better than the "be an alpha male" advice you might find on a lot of internet sites.

And here is advice specific to hard-driving successful men making relationships work:
https://beyond-driven.com/insideout1
"Discover The New Method That Hundreds Of Modern Men Have Used To Save Their Marriage, Reignite Their Sex Life, And Even Transform Their Careers... without ever going to marriage counseling, reading countless "self-help" books, or even mentioning a thing to their wife"

The core idea Tim Arrigo, guy behind that website, expresses in a related promo video is that the same conventional masculine traits that help me succeed in business (problem solving, suppressing emotions) lead to failures in their marriages. While I don't know the details of his approach, I've seen that theme before, like in the book "The Pleasure Trap" about how human behaviors to seek out salt, sweet, and fat (and conserve energy) that were so adaptive in our hunter/gatherer past lead to health disasters given our modern (processed) food supply. And I've also commented elsewhere on how people's traits that may help in one situation may hinder in another (like how paranoia may be useful for a programmer debugging complex code and being suspicious of every line but that paranoia may be corrosive in human relationships).

Many techies tend towards high-functioning Asperger's. If so, these may be of interest too, since relationships involving one or two Aspies can have some special dynamics:
https://duckduckgo.com/?q=aspergers+and+relationships

On the other hand, maybe you just have been lucky so far? :-) As in, from a Philip Greenspun essay:
https://philip.greenspun.com/careers/women-in-science
"Speaking of fertility... A $400/hour divorce litigator said "Knowing what I know now, I could have made a lot more money going to a bar and working for one night than I have made by going to college, law school, and working for 20 years. It turns out that I was sitting on something worth a lot more than a law degree." What's the cash value of fertility compared to working in science? ...
A divorce litigator put it a little more simply: "There is no reason for a woman to go to medical school. If she wants to have the spending power of a doctor she can just have sex with three doctors." ... In some states, though not Wisconsin, a plaintiff's own earnings or earning potential can reduce the potential profits from child support. "A degree in poetry is a lot better than a degree in medicine when you're a child support plaintiff," observed one litigator, and added "for a woman with a functioning reproductive system, the decision to attend college and work is seldom an economically rational one in the United States.""

No doubt there are various ways one can disagree with those selected divorce lawyer statements, of course. But they do suggest there can be potentially predatory "wrong women" out there if they believe those things. Of course, a woman in an unhappy relationship might also be more likely to drift in that direction of focusing on money? And the first links on building better relationships can help prevent that.

All the best in building mutually healthy relationships and raising a happy family if that is what you want.