Should i wish my Ex's sister happy birthday

Blessing

Please is it wise to wish my ex sister a happy birthday? We broke up last month June 23rd, Actually the last time we spoke (he just stopped communicating) after an unresolved problem. I also heard his step sister introduced him to a girl in her church and they have been going go church together. Today is his blood sisters birthday and we spoke twice over the phone in January and March this year.

They are very close and I don't want it to look like am seeking attention. Please what should I do? how do I get over him.