Never
Never
[Cueball staring into a pond.] Cueball: I know that no matter where I go Cueball: or who I build a life with
Cueball: I will never have with anyone Cueball: what I had with you
[Cueball walks off.] Cueball: Thank god

This comic plays with that some phrases are generally interpreted as communicating positive sentiments, although they strictly are ambiguous.
Cueball is mulling over a previous relationship. Usually when someone says something like "I will never have with anyone what I had with NN " it implies that the couple had something so good that it could never be replaced. But when he thinks "Thank God", it is suddenly implied that the relationship was so horrible he's thankful he'll never have to experience it again.
The title text goes along the same line: "I'll never forget you" is usually positive – but then it becomes clear that it is the red flags , the warning signs about the person that they would not be a good fit for a serious relationship and marriage, that he'll never forget.
There is a similar twist in comics 71: In the Trees and 334: Wasteland .
[Cueball staring into a pond.] Cueball: I know that no matter where I go Cueball: or who I build a life with
Cueball: I will never have with anyone Cueball: what I had with you
[Cueball walks off.] Cueball: Thank god
