yup, you're using default healing settings for Singular. You need to raise your healing percentages so the bot starts healing the second that the tank takes damage and doesn't stop if any character is below 99% health.
Once your gear starts getting better, you can play with the settings more, but for now, just change all your heals to cast above the 90% mark. Spefically:
Raise rejuv to 99%, raise swiftmend to 95%
Once you start getting more and more spells, add them in and change the percentages to match your level.