You don't have to believe in a certain deity. You don't have to subscribe to a religion or attend group ceremonies. You don't have to believe in one thing and stick to it.
You can be atheist, agnostic,
agnostic theist,
agnostic atheist, a devout Christian, Buddhist, Muslim, Hindu, ANYTHING.
If you believe that all things/beings are connected in some way, that the cosmos manifest the pattern of life, that science, truth, and openness to possibilities are essential, that there is something more to animals than physical mass and that love is a force that we to this day don't know everything about but live in awe of what life has to offer, you are spiritual.
People will always try to tell you to pick a team. To
cut the bullshit and stop saying your spiritual. Those people can also kiss your ass. And when they question your beliefs and intelligence, simply give them the okay to do so.