I started several projects, most of them I would not even call startups. Most of them unfinished, some failed, some successful.
I have tried several times to start something with a buddy from university, with him it's always the same: We talk about it, like the idea, I start to build it, he does not really join in and I lose motivation myself.
The one product which is the most profitable (or profitable at all if you factor in your own hours) is a rather lame one: A sitebuilder for small businesses. I buildt it while still in uni, lived off of it and literally put customers in one by one. Very stressful.
Another one I started after that with a an economics student, who had the initial idea. It was a dating app for students, when Tinder was on the rise in the US and had not gotten to Europe yet. I could not care less about that space, but I knew it was coming and I just wanted to start a real thing with a cofounder, which was totally different, so we did it. Collected a few hundred users from the local universities, ultimately failed, but I learned a few valuable lessons. It was nice having the cofounder around, but he could not really help at that point. He helped a bit with some guerilla marketing and started to work on our investment. I did the main work. That feeling of unfairness - even though you know that it is not on purpose, was really bad.
After that several other people approached me and I said no several times. I really wanted to build something in a team and have it play out. The feeling to fail alone is not good, but cofounders come with a different set of bad feelings. The failed attempts are costly, because you can only endure so much, before you need a success.
So I decided to approach my consulting as a startup and see the company with it's processes involved as the product. Have several employees and work with freelancers. I meet really interesting founders, I can learn from. I get approached to cofound all the time. I did not think that this would be enough, but really I already have the social interactions I was looking for in a cofounder. I just prefer to always have money exchanged for services. You can still be a good partners and maybe join in later, but I am a huge fan to simplify the relationship with payments. I even did some projects with the uni buddy, which work out great all the time.
The sitebuilder is still profitably tucking along. I know see it less as a lame project, which needs so much work, but as an asset and investment potential. Over the years it has brought in several nice opportunities.
To conclude: My solution sounds one-dimensional, but it really is "have a bit of money and success first". The more you have of it, the more interesting the conversations get. It is a nice filter, because people who have it are more likely to be successful again, plus they have the option to just pay you to build their ideas. You become able to do that yourself with yours. The relationships with your partners are just so much easier, you don't depend on the one perfect match, but different people can fulfil different roles, without the risk associated with a cofounder. Even your own projects appear in a better light and look nicer, when your time becomes more valuable.