Know What Love Is
One thing we forget to sustain in our attempt to love unconditionally are our personal boundaries. When opening ourselves up to love someone completely, we often end up losing ourselves in that process... to the detriment of our relationships.
Boundaries aren't walls; they do not act to limit intimacy or vulnerability. Boundaries allow you to be completely available to the extent that you can healthfully give of yourself at that time. They simultaneously act to limit and guard your space in times when you aren't capable of giving. Without boundaries, one feels they have to give and give to the point of depletion. This sacrifices you and your health, which will eventually lead to resentment.
Boundaries set standards for acceptable treatment. They in turn create space to communicate if and when those boundaries get impeded. When you feel there isn't space to communicate your needs or concerns, it's an indication that boundaries are not there.
Boundaries define interdependence; the relationship adds to your identity, but your identity isn't entirely absorbed by the definition of the relationship. This means separate friends are allowed, opposite sex friends are trusted, you participate in your own hobbies, and even time apart is encouraged and enjoyed. If you aren't allowed to have these things or any one of these bothers you or makes you jealous of your partner, again boundaries are missing.
Boundaries are invisible barriers formed by self love, respect and mutual trust. They keep you intact; as well as happy and healthy to participate fully in the relationship. Unconditional love embraces both the light and the dark, but also always knows where I end and you begin; as well as always respecting the needs and wants of both partners, never sacrificing one partner for the other.
Love others completely, love yourself equally.