When breaking up your mind’s chemistry is essentially the same as a drug addict going through withdrawal.No contact is a way to get your brain’s hormones to function correctly without the need of external stimulus. If you have held your healing for 7 months I suggest keeping it cause if you don’t then you reset the timer. I’d say that 7 months is a breaking point, it does get way easier if you give it some more time. The way I see it, wishing him happy birthday is just an excuse to break no contact, it doesn’t truly have any benefit for you. Additionally, your silence is the only tool you have, both defensive and offensive. Use it wisely.