Stressed everyday! Father in law lives with us, huge jerk! I'm diagnosed with severe anxiety. Breastfeeding 1 year old. Does this affect my breastmilk?

Absolutely. We do not pay enough attention to the mind-body connection. Stress can affect every aspect of your life, including milk production and thus breastfeeding. Get some help in dealing with these issues. It will ultimately be helpful to you, your baby, your husband, and your father-in-law.
It can affect both. Your milk flow &, more importantly, your emotional availability to your toddler. If you wish, you can wean to an open-mouthed, doubled handled cup, limiting cow's milk & milk products to 16-21 oz./day. Like airline attendants say, put on your own oxygen mask before helping your child. You'll benefit from medication, cognitive-behavioral therapy, & speaking openly to your husband about this.
Part of you. Your baby is an extension of you - your body and your mood. Your baby with sense your anxiety and tension. Your milk may not flow well and can contain stress hormones. But your touch and feel and smell will also be sensed by your baby. The entire atmosphere he lives in is affecting your child. You must discuss this with all members in the household.
Effects you. You baby will sense you are stressed--best thing you can do for baby is feel good yourself--may need a father in law ectomuy! (:.