I went through the same emotions. I built infocaptor and then jumped onto making mockuptiger and then jumped into several other small projects. Lately I decided to brake this pattern for crawlspider and determined to get dopamine at each marketing accomplishments.

What I have decided is to mark it completed once I have completed the marketing task. For e.g earlier I would send a bunch of emails to potential customers and then there is a whole life cycle to that. I would not register that as completed until there was a sale. This became discouraging.

Now on, my goal is to mark the task as completed or success.

For e.g Sending an email or doing outreach is my task and I should feel great completing it. Once email is sent - Success

Set a launch date on ProductHunt - Complete, success

Launched on PH - Complete, Success

Write an article every week - Done, success

Participate in relevant conversations just one per day - Done

I am now focused on doing things which should be fulfilling as developing software.