Well, he had this girlfriend--okay, he and his symbiote had a girlfriend in her symbiote, in a complicated, two-body/four-personality poly relationship--and the girlfriend and symbiote disappeared, and then he found out that the symbiote had briefly survived the girlfriend in Sam's head but now they were both dead and Sam was all that was left, and Sam wouldn't take a symbiote (even though she looked a lot like his dead girlfriend, and he was hoping she would!) and she wouldn't even date him because she was all confused, and on a scale of Sam's boyfriends he actually took all of this in a calm and non-stalkery manner, and then he got captured and brainwashed by the Goa'uld and sent to assassinate the President of the US, and so he ended up having to beg Sam to shoot him dead before he committed suicide, which she did, in that episode where Jack and Sam were all "uh, I care about you more than I should."

So, really, Poor Martouf. Died for the greater glory of the Jack/Sam.