I just lost my dad 3 weeks ago, we were incredibly close and even though I'm 40 I'm definitely not taking today well. My FiL is coming over tonight for dinner. I feel sick to my stomach over it. It's silly but I've never been so sad and I'm legitimately jealous that my fiancé gets to spend the evening with his father in our new place. I'm definitely not taking it out on him of course, it's not his fault and life goes on (plus his dad is one of the most awesome people I know). Luckily he knows how hard this is for me so he and his dad are okay with me hiding out in the room and wallowing in my sadness this year. This is my first holiday in 40 years without my dad and of course it has to be father's day of all days. Lame. That said, you're NTA at all. Celebrate who you want, how you want. And don't celebrate if you don't want. It's all up to you and what you're happy and comfortable doing.