Tá grá agam duit means "I love you" (lit. "There is love at me with you). Go deo means forever. So, altogether it's "I love you forever." This isn't the most correct way of saying this, obviously,...
It doesn't make sense but it was likely meant to be "Tá mé i ngrá leat". 'Tá mé i ngrá leat' means 'I'm in love with you'.google translator can't do Irish.