The only problem here is that the author perceives a need to apologize, or to even feel regret. If the only compensation for starting and maintaining an open source project is the work itself or personal use of the product, then you are your only customer. The moment it stops being fun or worth the effort, you have every right to just stop without feeling a tiny bit of guilt or remorse.

You have a bug they want to fix or a feature they want to add and the author/maintainer is not doing it fast enough? Fork away! Submit a pull request! Oh, you don't have the skills/time to do that? Wow, that's too bad. Offer to pay the author! Post a message to the project list or bug reporting tool offering to pay someone to do it for you. Oh, you want it for free? Immediately? You built critical infrastructure around a tool you don't understand and don't have the skills or resources to maintain? You're a parasite, and can be safely muted and ignored.

This is the important bit: If you're afraid the person maintaining your key infrastructure for free might suddenly stop doing that, just take some time to send them a nice note thanking them. Periodically getting one of those in your inbox is remarkably effective in maintaining passion for a project. Find a way to give them a gift. Do they have Venmo/Patreon/Amazon wish list? Use it. Are you a developer or do you employ some? Fix a bug. Say nice things about them in social media. Offer to help pay for the resources to host the project. Send them an effing Starbuck's card with your sincere thanks.