How do I know if i'm being attacked?
Detection of de-auth frames can be difficult to spot, you'll need software like nzyme (which is WI-FI monitoring software) along with something like Graylog, a WI-FI security management tool. Graylog enables you to analyze the wireless traffic hitting your network.
You'll find a much better explanation of each by just Googling the above software.
The above may help you identify if you are the target of such attacks.
With regards to preventing it, there is no definite way of preventing de-authentication attacks.
If your AP supports it, you can enable 802.11w which increases the security of management frames and can assist with preventing these types of attacks, move info here:(802.11w)
Some people may suggest hiding your SSID. If your neighbor has a network card capable of injecting packets along with the know-how to send de-auth attacks, chances are he'll be able to suss out and discover you've hidden your SSID pretty quickly.
I can appreciate the pure annoyance of this is the entire point of wanting to block these attacks, however, these types of attacks can be much more devastating in somewhere like a coffee shop for instance, so I wouldn't be too concerned with regards to network security. (This doesn't take away from the fact this person still of course has the ability to try capturing the handshake and attempting a brute-force, see below for suggestion on how to near-eradicate this worry).
If this is your home network the best thing you can do if you are worried would be to create a strong, long password. Generate a 20 char one if needs be, just don't forget it!