Discuss your "dealbreakers" – would it be dating the other friend's ex? When do each of you feel comfortable speaking up when differences arise? Immediately? Or do you tend to sit on your emotions? It's essential to any friendship not to be the friend who uses the other one emotionally. Friends are there to lean on, but when one gives support freely while the other habitually takes it without returning support, then conflict can arise. Venting is OK when both parties are OK with it, but your friend shouldn't become your personal emotional dumping ground.  Both of you have lives and face conflicts, but it's important to balance your relationship with lighthearted, fun stuff, too.