Another pitfall with this approach is when someone has constant emotional but irrational reactions to everything. Being the person who validates their emotions becomes harmful if they’re over-reacting or developing harmful emotional reactions and you’re always there to validate them.

If it becomes damaging to you (the person that is expected to be emotional support), "grey rocking" is the next step. Acknowledge, but don't respond. "uh huh" instead of "I am so sorry" or whatever. Don't take advice from me though.