How can I avoid my-guy-syndrome after devastating battle

We are a group of three players. Me (a priest of the goddess of healing and agriculture), Alice (priest of the god of light/time/law) and fighter-archetype Bob.

Our last evening went as follows. The previous evening I and Bob coerced an NPC ("John") to gather information for us and to meet with us the following day in the ghetto before a city. I went there alone, as Alice and Bob attended some other business and I didn’t want to miss our informant. When I arrived, another NPC told me

You have to hurry. John was already here. He told me it was urgent and to tell you he’ll meet you in the forest. And he was bleeding, it looked bad!

Concerned as a healer about the wounded man, I immediately followed. After following the trail for quite some long time, I had a critical miss-roll and got lost in the forest, until I rejoined with my comrades, which ultimately followed. We finally arrived at an obvious ambush, where John was lying on the ground, with a gaping wound on the back (shoulder blades were visible), on the brink of death, but still breathing. As I was unarmed, I ignored the imminent danger and immediately went to him to try to save his life, assuming the enemy wouldn’t attack an unarmed priest. A battle ensued nontheless. Due to severely unlucky dice rolls, our 2nd priest got one-shotted (down to low health, bleeding and unconscious). Our fighter-archetype had gone around the group and attacked from behind. I was also attacked, but defended by my dogs. After the first dog was killed, I retreated hastily, without completing the healing ritual that would have saved both John and Alice.

Although Alice was rescued by the rogue boss (healing potion…go figure), my character presumes her dead, as this happened after she fled. Furthermore, she believes the important people of the city are behind this attack, to save the secret John had discovered. Thus it now seems logical to me, to leave this place behind, as going back to the city seems like certain death (you can only enter through the gates, so going in unseen is not an option).

I don’t want this to be a my-guy-syndrome situation, but how can I plausibly not abandon the group and the city? I already told the GM that I need some time to think about my next move, because of the situation above.