Seau was 43-years-old ... and leaves behind 3 kids and an ex-wife.
Cops are currently at Seau's home -- located in San Diego County -- and were seen talking with a man who was inside the house and appeared distraught.
We're told Seau sent text messages to his ex-wife and 3 kids yesterday saying, "Love you." We're told they all responded and didn't suspect anything was wrong. We're told he last saw his kids 3 weeks ago.