On the "father & son" side of the debate, I must admit that there is a scene in "Picaros" which I think bears this out: on the page where Haddock announces that they are going to San Theodoros and have it out with Tapioca, Tintin stands there with hands on his hips as if bemused and then, giving Haddock a hard stare, announces "You may be going... I'm staying!"
Of course, he points out the practical reasons, like the whole thing being a trap (which it is) and, when he himself turns up in South America, the desire to get their friends out of jail. On the other hand though, you could say that this is the attitude of a young man trying to break free from his parents: like his statement is really "I'll go in my own time, not when you tell me to, 'Dad'!"
Of course, Tintin was very independent before and after he had met Haddock, but certainly since "Destination Moon" they had travelled the world (and space) practically stuck to each other like glue, so this could be Herge's way of reminding us that they are still free agents (and giving Haddock more focus in what Herge himself quite likely saw as his last adventure).
Other than that, I stand by my view that Tintin and Haddock are just friends who enjoy each other's company. I very much doubt that Herge intended to imply anything sexual, even subconciously. As I indicated in a previous post
this was not unusual element in Belgian comics of the time.
Rather, like the other series, I see Tintin's presence at Marlinspike being more practical plot-wise. After all, it would slow down the action if he kept travelling between Marlinspike and his own flat in town as he does in "Crystal Balls". The plot in "Castafiore Emerald" (which I consider one of the weakest) would have been weaker still had we had Tintin investigating from town at a distance or having to commute on an almost daily basis.