When a self-absorbed desert-trawling truckie falls for a devoted mother and city writer online, he must take responsibility for his own son, before winning her heart or losing his last chance for true love.

Thanks Nir, I think it is definitely time for me to attend one of your analysis meetups :-)

"...he wants her love but he can't even love his own son so he needs to be able to?love (and take responsibility for) his own flesh and blood before he can truly love anyone else ..."

This is not a cause and effect, it's a statement that you made in retrospect. If you were to ask any person the following:
If a long-haul trucker falls in love with a writer in the city, what do you think he should do?
The answer would be: well obviously he needs to drive from the desert to the city and go after the woman.
The answer would not be: well obviously he needs to take responsibility for and love his own son.

The two actions simply don't add up to the goal you're trying to have him pursue. He can have a subplot in which he patches up a broken relationship with his estranged son, but it's not a part of the main ('A') plot and therefore shouldn't be in the logline.

Cause and effect need to be inherent in the combination of events and actions, and the obstacles need to be cinematic not just internal emotions.

I suggest you think outside the box to find a better obstacle standing in his way from getting the girl, then devise a set of visual actions that will convey his pursuit of the goal. What if, he's stuck on a 5 day trip from one side of the country to the other, and he gets the news that the love of his life is about to move overseas in 4 days. He now has to drive his loads faster than he should in order to get to her before she leaves forever.

Hi guys, thank you all so much for your comments. It's given me lots to think about.
Russell, you're right ? 90-year-olds do fall in love! Why her specifically? I have some corny ideas about kismet moments and reminders of a dead lover ??.. but I'm not sure beyond that.
Paul, thanks, your suggested logline is so much better than mine in capturing what the story is about.
Nir, I have given some thought to your questions and perhaps 'taking responsibility' is not the main flaw that he has to deal with (but is a secondary flaw maybe). The cause and effect is that he wants her love but he can't even love his own son so he needs to be able to?love (and take responsibility for) his own flesh and blood before he can truly love anyone else (otherwise it's just self-absorbed, selfish 'love'.) How that could look could be taking his son on the road with him (maybe to help him with a job and get him away from drugs/foster care) rather than ignoring his son and obsessing about getting the girl on the road. So maybe, something along these lines ?

When a self-absorbed long-haul trucker falls for a big city writer, he must learn to love and include his estranged son in his world, before he can win her heart.

?To win the heart of a big city writer by getting her to fall in love with the road, a self-absorbed long-haul trucker must first learn to love and take responsibility for his estranged son by including him in his world.