I'm probably going to shock some people, but Heart Problems is a pure harem VN! And she doesn't even have many options. I've tried everything, but nothing has helped. The following list is the naked truth:
Lauren solo route: no
Ignore Lauren: no
Mia solo route: no
Ignore Mia: yes???
Stephanie solo route: no
Ignore Stephanie: yes
Kylee solo route: no
Ignore Kylee: no
Amelie solo route: no
Ignore Amelie: no
As you can see, a solo route isn't possible and probably not even planned. If you only take Amelie and Kylee, this VN is even a KN (kinetic novel). Except for one very specific decision (whether you confess your love to Amelie or keep it a secret), it doesn't matter what answers you give. Even with 0 lust and/or love points, you'll be able to fuck Kylee's brains out and do anything with Amelie, probably even fuck her in EP 11. Starting at EP 5 or 6 (hit with Death), there are no more route-deciding decisions.
Conclusion:
If you HAVE to play harem, then take everyone along and have fun.