How would I ever know if my therapist is there for me?

Available therapist. It's unclear from your question whether you intend to ask whether your therapist will be there for you emotionally or physically. If it's the latter, check with him/her about office hrs, emergencies, on call policies. Also discuss whatever concerns you might have about him/her not being there for you. This might be a needed component of your therapy re: possible reject and/or abandonment issues.